ANDROID: KVM: arm64: pkvm: Rework sysreg entry/exit handling

Rework the sysreg entry/exit handling for protected guests so that:

  - The host view of the vCPU pstate is updated on exit, as this may be
    required for emulation
  - WRITE_ONCE() is used to update host vCPU members
  - The esr_sys64_to_params() helper is used to decode the ESR
  - A pending exception request from the host takes precedence over a PC
    increment when setting the shadow vCPU flags

Signed-off-by: Marc Zyngier <maz@kernel.org>
Bug: 209580772
Change-Id: Ia9b546f86a8815d777b3ff4ee3b09426cba7ad71
Signed-off-by: Will Deacon <willdeacon@google.com>