x86/sev: Let sev_es_efi_map_ghcbs() map the CA pages too

OVMF EFI firmware needs access to the CA page to do SVSM protocol calls. For
example, when the SVSM implements an EFI variable store, such calls will be
necessary.

So add that to sev_es_efi_map_ghcbs() and also rename the function to reflect
the additional job it is doing now.

  [ bp: Massage. ]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250626114014.373748-4-kraxel@redhat.com