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 <julianbraha@gmail.com>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Link: https://lore.kernel.org/r/20211215214022.146391-1-julianbraha@gmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>