pinctrl: STMFX: add missing HAS_IOMEM dependency

pinctrl: STMFX: add missing HAS_IOMEM dependency

When building on ARCH=um (which does not set HAS_IOMEM), kconfig
reports an unmet dependency caused by PINCTRL_STMFX. It selects
MFD_STMFX, which depends on HAS_IOMEM. To stop this warning,
PINCTRL_STMFX should also depend on HAS_IOMEM.

kconfig warning:
WARNING: unmet direct dependencies detected for MFD_STMFX
  Depends on [n]: HAS_IOMEM [=n] && I2C [=y] && OF [=y]
  Selected by [y]:
  - PINCTRL_STMFX [=y] && PINCTRL [=y] && I2C [=y] && OF_GPIO [=y]

Fixes: 1490d9f841b1 ("pinctrl: Add STMFX GPIO expander Pinctrl/GPIO driver")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/20250815022721.1650885-1-rdunlap@infradead.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>