clocksource/drivers/timer-microchip-pit64b: Remove mmio selection

PIT64B timer driver doesn't depend on CLKSRC_MMIO since
commit e85c1d21 ("clocksource/drivers/timer-microchip-pit64b:
Add clocksource suspend/resume"). Remove the selection.
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220304133601.2404086-2-claudiu.beznea@microchip.comSigned-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/Kconfig

@@ -713,7 +713,6 @@ config INGENIC_OST
 config MICROCHIP_PIT64B
 	bool "Microchip PIT64B support"
 	depends on OF || COMPILE_TEST
-	select CLKSRC_MMIO
 	select TIMER_OF
 	help
 	  This option enables Microchip PIT64B timer for Atmel