arm64: cpufeature: Fix meta-capability cpufeature check

Some existing/future meta cpucaps match need the presence of individual
cpucaps. Currently the individual cpucaps checks it via an array based
flag and this introduces dependency on the array entry order.
This limitation exists only for system scope cpufeature.

This patch introduces an internal helper function (__system_matches_cap)
to invoke the matching handler for system scope. This helper has to be
used during a narrow window when,
- The system wide safe registers are set with all the SMP CPUs and,
- The SYSTEM_FEATURE cpu_hwcaps may not have been set.

Normal users should use the existing cpus_have_{const_}cap() global
function.

Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>