ANDROID: KVM: arm64: s2mpu: Fix SYNC latency regression

SysMMU_SYNCs provide an invalidation-complete signal to the S2MPU
driver but the latency can be quite high. Improve this by waiting for
all the SYNCs in parallel - separate the initiation of invalidation
barrier from waiting for completion. This way we initiate invalidation
on all SYNCs first, then wait for all of them to complete.

The previously introduced exponential-backoff only kicks in if the
SYNC_COMP_COMPLETE bit is not set after the parallel invalidation.

Bug: 249161451
Signed-off-by: David Brazdil <dbrazdil@google.com>
Change-Id: I9d544bc65f8633d376c7ccd65ea23195ca432964
(cherry picked from commit 1da102d4)
Signed-off-by: Mostafa Saleh <smostafa@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>