KVM: arm64: Restore host physical timer access on hyp_panic()

KVM: arm64: Restore host physical timer access on hyp_panic()

When KVM panics, it hurridly restores the host context and parachutes
into the host's panic() code. At some point panic() touches the physical
timer/counter. Unless we are an arm64 system with VHE, this traps back
to EL2. If we're lucky, we panic again.

Add a __timer_save_state() call to KVMs hyp_panic() path, this saves the
guest registers and disables the traps for the host.

Fixes: 53fd5b6487e4 ("arm64: KVM: Add panic handling")
Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Christoffer Dall <cdall@linaro.org>