KVM: arm64: Correctly access TCR2_EL1, PIR_EL1, PIRE0_EL1 with VHE

KVM: arm64: Correctly access TCR2_EL1, PIR_EL1, PIRE0_EL1 with VHE

For code that accesses any of the guest registers for emulation
purposes, it is crucial to know where the most up-to-date data is.

While this is pretty clear for nVHE (memory is the sole repository),
things are a lot muddier for VHE, as depending on the SYSREGS_ON_CPU
flag, registers can either be loaded on the HW or be in memory.

Even worse with NV, where the loaded state is by definition partial.

For these reasons, KVM offers the vcpu_read_sys_reg() and
vcpu_write_sys_reg() primitives that always do the right thing.
However, these primitive must know what register to access, and
this is the role of the __vcpu_read_sys_reg_from_cpu() and
__vcpu_write_sys_reg_to_cpu() helpers.

As it turns out, TCR2_EL1, PIR_EL1, PIRE0_EL1 and not described
in the latter helpers, meaning that the AT code cannot use them
to emulate S1PIE.

Add the three registers to the (long) list.

Fixes: 86f9de9db178 ("KVM: arm64: Save/restore PIE registers")
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Joey Gouly <joey.gouly@arm.com>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/r/20241023145345.1613824-9-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>