ARM: soc: dependency warnings for errata

The PL310_ERRATA_753970 and ARM_ERRATA_764369 symbols only make sense
when the base features for them are enabled, so select them
conditionally in Kconfig to avoid warnings like:

warning: (UX500_SOC_COMMON) selects PL310_ERRATA_753970 which has unmet direct dependencies (CACHE_PL310)
warning: (ARCH_TEGRA_2x_SOC && ARCH_TEGRA_3x_SOC && UX500_SOC_COMMON) selects ARM_ERRATA_764369 which has unmet direct dependencies (CPU_V7 && SMP)

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Stephen Warren <swarren@nvidia.com>