ARM: realview: Drop unneeded select of multi-platform features

Support for ARM Ltd. RealView systems depends on ARCH_MULTIPLATFORM,
which selects USE_OF.
Support for ARMv6 and ARMv7 variants depends on ARCH_MULTI_V6 or
ARCH_MULTI_V7, which both select ARCH_MULTI_V6_V7 and thus
MIGHT_HAVE_CACHE_L2X0.
Support for ARMv7 variants depends on ARCH_MULTI_V7, which selects
HAVE_SMP.
Hence there is no need for the affected RealView-specific symbols to
select any of them.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>