KVM: arm64: Clarify the check for reset callback in check_sysreg_table()

KVM: arm64: Clarify the check for reset callback in check_sysreg_table()

check_sysreg_table() has a wonky 'is_32" parameter, which is really
an indication that we should enforce the presence of a reset helper.

Clean this up by naming the variable accordingly and inverting the
condition. Contrary to popular belief, system instructions don't
have a reset value (duh!), and therefore do not need to be checked
for reset (they escaped the check through luck...).

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Sebastian Ott <sebott@redhat.com>
Link: https://lore.kernel.org/r/20250718111154.104029-3-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>