KVM: selftests: Move XSAVE and OSXSAVE CPUID checks into AMX's init_regs()

Move the checks on XSAVE and OSXSAVE into init_regs() so that the XSAVE
check is done before setting CR4.OSXSAVE, i.e. before a potential #GP, and
so that the OSXSAVE check is performend immediately after enabling XSAVE
in CR4.

Signed-off-by: Aaron Lewis <aaronlewis@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
Link: https://lore.kernel.org/r/20230221163655.920289-12-mizhang@google.com


[sean: keep XSAVE check, rewrite changelog accordingly]
Signed-off-by: Sean Christopherson <seanjc@google.com>