pinctrl: aspeed: fix unmet dependencies on MFD_SYSCON for PINCTRL_ASPEED

When PINCTRL_ASPEED_G* is selected,
and MFD_SYSCON is not selected,
Kbuild gives the following warnings:

WARNING: unmet direct dependencies detected for PINCTRL_ASPEED
Depends on [n]: PINCTRL [=y] && (ARCH_ASPEED [=n] || COMPILE_TEST [=y]) && OF [=y] && MFD_SYSCON [=n]
Selected by [y]:
- PINCTRL_ASPEED_G4 [=y] && PINCTRL [=y] && (MACH_ASPEED_G4 [=n] || COMPILE_TEST [=y]) && OF [=y]

WARNING: unmet direct dependencies detected for PINCTRL_ASPEED
Depends on [n]: PINCTRL [=y] && (ARCH_ASPEED [=n] || COMPILE_TEST [=y]) && OF [=y] && MFD_S>
Selected by [y]:
- PINCTRL_ASPEED_G5 [=y] && PINCTRL [=y] && (MACH_ASPEED_G5 [=n] || COMPILE_TEST [=y]) && O>

WARNING: unmet direct dependencies detected for PINCTRL_ASPEED
Depends on [n]: PINCTRL [=y] && (ARCH_ASPEED [=n] || COMPILE_TEST [=y]) && OF [=y] && MFD_S>
Selected by [y]:
- PINCTRL_ASPEED_G6 [=y] && PINCTRL [=y] && (MACH_ASPEED_G6 [=n] || COMPILE_TEST [=y]) && O>

This is because MACH_ASPEED_G* depend on (ARCH_ASPEED || COMPILE_TEST).
ARCH_ASPEED enables the MFD_SYSCON dependency, but COMPILE_TEST doesn't.

These unmet dependency bugs were detected by Kismet,
a static analysis tool for Kconfig. Please advise
if this is not the appropriate solution.

Signed-off-by: Julian Braha <[e-mail]>
Reviewed-by: Andrew Jeffery <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Linus Walleij <[e-mail]>

drivers/pinctrl/aspeed/Kconfig

···
 config PINCTRL_ASPEED
 	bool
 	depends on (ARCH_ASPEED || COMPILE_TEST) && OF
-	depends on MFD_SYSCON
+	select MFD_SYSCON
 	select PINMUX
 	select PINCONF
 	select GENERIC_PINCONF