KVM: arm64: Convert timer offset VA when accessed in HYP code

Now that EL2 has gained some early timer emulation, it accesses
the offsets pointed to by the timer structure, both of which
live in the KVM structure.

Of course, these are *kernel* pointers, so the dereferencing
of these pointers in non-kernel code must be itself be offset.

Given switch.h its own version of timer_get_offset() and use that
instead.

Fixes: b86fc215 ("KVM: arm64: Handle counter access early in non-HYP context")
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Tested-by: Anders Roxell <anders.roxell@linaro.org>
Link: https://lore.kernel.org/r/20250212173454.2864462-1-maz@kernel.org


Signed-off-by: Marc Zyngier <maz@kernel.org>