arm64: Kconfig: select PM{,_GENERIC_DOMAINS} for ARCH_VEXPRESS

The Linux AMBA bus framework probes the peripheral IDs when adding the
AMBA devices very early on the boot. Generally they are on APB bus and
just require APB clocks to be on even when most of the core logic of the
IP is powered down.

However on Juno, the entire debugsys domain needs to be ON to access
even the coresight components' CID/PID registers and hence broken by
design. Accessing those while debugsys power domain is off will lead to
the bridge stalling the transactions instead of returning the slave error.

Further, the AMBA framework can't deal with !CONFIG_PM_GENERIC_DOMAINS
case: it ignores the error and proceeds to access the device region.
It was suggested to always enable CONFIG_PM{,_GENERIC_DOMAINS} in order
to handle above explained scenario.

Cc: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Olof Johansson <olof@lixom.net>