ANDROID: KVM: arm64: s2mpu: Move mpt_update_flags into FMPT

Core SMPT manipulation code returns mpt_update_flags, signalling whether
the caller should flush the dcache (MPT_UPDATE_L2) or write new L1ATTR
values to S2MPU MMIO registers (MPT_UPDATE_L1).

In preparation for splitting the code into a driver-global and
per-device portions, store the value in the corresponding FMPT.
As long as the two code portions are called from a single critical
section, the FMPT value is guaranteed to not change.

Bug: 190463801
Signed-off-by: David Brazdil <dbrazdil@google.com>
Change-Id: Iec06697e8826b0dba682476b39cf64acd6337166