Revert "ARM: vexpress: Don't select VEXPRESS_CONFIG"

This reverts commit 848685c2.
Due to when I set 'depends on VEXPRESS_CONFOG=Y' in 'config
POWER_RESET_VEXPRESS' to get an allmodconfig build on arm64 to build,
and allmodconfig build on arm fails if this patch isn't reverted.

Link: https://lore.kernel.org/r/20200527112608.3886105-4-anders.roxell@linaro.org


Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>