UPSTREAM: KVM: arm64: Macros for setting/clearing FGT bits

There's a lot of boilerplate code for setting and clearing FGT
bits when activating guest traps. Refactor it into macros. These
macros will also be used in future patch series.

No functional change intended.

Bug: 278749606
Change-Id: I1b731e3ac1681987d868c5a16b74f2481a8e219d
Signed-off-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231214100158.2305400-15-tabba@google.com
(cherry picked from commit 0ccd901d)