KVM: arm64: Initialize PMSCR_EL1 when in VHE

KVM: arm64: Initialize PMSCR_EL1 when in VHE

According to the pseudocode for StatisticalProfilingEnabled() from Arm
DDI0487L.b, PMSCR_EL1 controls profiling at EL1 and EL0:

- PMSCR_EL1.E1SPE controls profiling at EL1.
- PMSCR_EL1.E0SPE controls profiling at EL0 if HCR_EL2.TGE=0.

These two fields reset to UNKNOWN values.

When KVM runs in VHE mode and profiling is enabled in the host, before
entering a guest, KVM does not touch any of the SPE registers, leaving the
buffer enabled, and it clears HCR_EL2.TGE. As a result, depending on the
reset value for the E1SPE and E0SPE fields, KVM might unintentionally
profile a guest. Make the behaviour consistent and predictable by clearing
PMSCR_EL1 when KVM initialises the host debug configuration.

Note that this is not a problem for nVHE, because KVM clears
PMSCR_EL1.{E1SPE,E0SPE} before entering the guest.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Link: https://lore.kernel.org/r/20250902130833.338216-2-alexandru.elisei@arm.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>