ARM: imx: select PINCTRL at sub-architecure level

Instead of selecting PINCTRL on individual SoC, let's select it at IMX
sub-architecure level.

While at it, it also adds the missing PINCTRL_IMX50 selection for
SOC_IMX50.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/mach-imx/Kconfig

@@ -11,6 +11,7 @@ config ARCH_MXC
 	select GENERIC_IRQ_CHIP
 	select MIGHT_HAVE_CACHE_L2X0 if ARCH_MULTI_V6_V7
 	select MULTI_IRQ_HANDLER
+	select PINCTRL
 	select SOC_BUS
 	select SPARSE_IRQ
 	select USE_OF
@@ -99,7 +100,6 @@ config SOC_IMX25
 	select ARCH_MXC_IOMUX_V3
 	select CPU_ARM926T
 	select MXC_AVIC
-	select PINCTRL
 	select PINCTRL_IMX25
 
 config SOC_IMX27
@@ -110,7 +110,6 @@ config SOC_IMX27
 	select IMX_HAVE_IOMUX_V1
 	select MACH_MX27
 	select MXC_AVIC
-	select PINCTRL
 	select PINCTRL_IMX27
 
 config SOC_IMX31
@@ -139,7 +138,6 @@ config SOC_IMX5
 config	SOC_IMX51
 	bool
 	select HAVE_IMX_SRC
-	select PINCTRL
 	select PINCTRL_IMX51
 	select SOC_IMX5
 
@@ -763,6 +761,7 @@ comment "Device tree only"
 config	SOC_IMX50
 	bool "i.MX50 support"
 	select HAVE_IMX_SRC
+	select PINCTRL_IMX50
 	select SOC_IMX5
 
 	help
@@ -772,7 +771,6 @@ config	SOC_IMX53
 	bool "i.MX53 support"
 	select HAVE_IMX_SRC
 	select IMX_HAVE_PLATFORM_IMX2_WDT
-	select PINCTRL
 	select PINCTRL_IMX53
 	select SOC_IMX5
 
@@ -798,7 +796,6 @@ config SOC_IMX6Q
 	select MFD_SYSCON
 	select MIGHT_HAVE_PCI
 	select PCI_DOMAINS if PCI
-	select PINCTRL
 	select PINCTRL_IMX6Q
 	select PL310_ERRATA_588369 if CACHE_PL310
 	select PL310_ERRATA_727915 if CACHE_PL310
@@ -819,7 +816,6 @@ config SOC_IMX6SL
 	select HAVE_IMX_MMDC
 	select HAVE_IMX_SRC
 	select MFD_SYSCON
-	select PINCTRL
 	select PINCTRL_IMX6SL
 	select PL310_ERRATA_588369 if CACHE_PL310
 	select PL310_ERRATA_727915 if CACHE_PL310
@@ -833,7 +829,6 @@ config SOC_VF610
 	select CPU_V7
 	select ARM_GIC
 	select CLKSRC_OF
-	select PINCTRL
 	select PINCTRL_VF610
 	select VF_PIT_TIMER
 	select PL310_ERRATA_588369 if CACHE_PL310