docs: driver-api: gpio: Fix filename mismatch

The filenames were changed a while ago, but board.rst, consumer.rst and
intro.rst still refer to the old names. Fix those references to match the
Actual names and avoid possible confusion.
Signed-off-by: Tom Schwindl <schwindl@posteo.de>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>

Documentation/driver-api/gpio/board.rst

@@ -6,7 +6,7 @@ This document explains how GPIOs can be assigned to given devices and functions.
 
 Note that it only applies to the new descriptor-based interface. For a
 description of the deprecated integer-based GPIO interface please refer to
-gpio-legacy.txt (actually, there is no real mapping possible with the old
+legacy.rst (actually, there is no real mapping possible with the old
 interface; you just fetch an integer from somewhere and request the
 corresponding GPIO).
 

Documentation/driver-api/gpio/consumer.rst

@@ -4,7 +4,7 @@ GPIO Descriptor Consumer Interface
 
 This document describes the consumer interface of the GPIO framework. Note that
 it describes the new descriptor-based interface. For a description of the
-deprecated integer-based GPIO interface please refer to gpio-legacy.txt.
+deprecated integer-based GPIO interface please refer to legacy.rst.
 
 
 Guidelines for GPIOs consumers
@@ -78,7 +78,7 @@ whether the line is configured active high or active low (see
 
 The two last flags are used for use cases where open drain is mandatory, such
 as I2C: if the line is not already configured as open drain in the mappings
-(see board.txt), then open drain will be enforced anyway and a warning will be
+(see board.rst), then open drain will be enforced anyway and a warning will be
 printed that the board configuration needs to be updated to match the use case.
 
 Both functions return either a valid GPIO descriptor, or an error code checkable
@@ -270,7 +270,7 @@ driven.
 The same is applicable for open drain or open source output lines: those do not
 actively drive their output high (open drain) or low (open source), they just
 switch their output to a high impedance value. The consumer should not need to
-care. (For details read about open drain in driver.txt.)
+care. (For details read about open drain in driver.rst.)
 
 With this, all the gpiod_set_(array)_value_xxx() functions interpret the
 parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line

Documentation/driver-api/gpio/intro.rst

@@ -14,12 +14,12 @@ Due to the history of GPIO interfaces in the kernel, there are two different
 ways to obtain and use GPIOs:
 
   - The descriptor-based interface is the preferred way to manipulate GPIOs,
-    and is described by all the files in this directory excepted gpio-legacy.txt.
+    and is described by all the files in this directory excepted legacy.rst.
   - The legacy integer-based interface which is considered deprecated (but still
-    usable for compatibility reasons) is documented in gpio-legacy.txt.
+    usable for compatibility reasons) is documented in legacy.rst.
 
 The remainder of this document applies to the new descriptor-based interface.
-gpio-legacy.txt contains the same information applied to the legacy
+legacy.rst contains the same information applied to the legacy
 integer-based interface.