x86/altp2m: clean up p2m_{get/set}_suppress_ve()

x86/altp2m: clean up p2m_{get/set}_suppress_ve()

Move p2m_{get/set}_suppress_ve() to p2m.c, replace incorrect
ASSERT() in p2m-pt.c (since a guest can run in shadow mode even on
a system with virt exceptions, which would trigger the ASSERT()),
move the VMX-isms (cpu_has_vmx_virt_exceptions checks) to
p2m_ept_{get/set}_entry(), and fix locking code in
p2m_get_suppress_ve().

Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>