ANDROID: KVM: arm64: Allow tweaking HFGWTR_EL2 from modules

pKVM modules may need to enable fine grain traps. To allow this
use-case, expose a function allowing to manipulate HFGWTR_EL2 on the
current CPU. This configuration will be persistent across power
management cycles and such as it is propagated all the way to the
init params per-cpu struct.

Bug: 245034629
Change-Id: If9c29849df50847d3a796345927bd51c37c358bc
Signed-off-by: Quentin Perret <qperret@google.com>