arm64: cpufeatures: Add missing ID_AA64MMFR4_EL1 to __read_sysreg_by_encoding()

arm64: cpufeatures: Add missing ID_AA64MMFR4_EL1 to __read_sysreg_by_encoding()

When triggering a CPU hotplug scenario, we reparse the CPU feature
with SCOPE_LOCAL_CPU, for which we use __read_sysreg_by_encoding()
to get the HW value for this CPU.

As it turns out, we're missing the handling for ID_AA64MMFR4_EL1,
and trigger a BUG(). Funnily enough, Marek isn't completely happy
about that.

Add the damn register to the list.

Fixes: 805bb61f8279 ("arm64: cpufeature: Add ID_AA64MMFR4_EL1 handling")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240212144736.1933112-2-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>