ARM: fix XIP_KERNEL dependencies

CONFIG_XIP_KERNEL does not work with any option that involves patching
the read-only kernel .text.

Since at least CONFIG_SMP_ON_UP is required in certain configurations,
flip the dependency to always allow the .text patching options but make
XIP_KERNEL have the dependency instead.

This is a prerequisite for allowing CONFIG_ARCH_MULTIPLATFORM to
be disabled.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>