[efi] Ignore failures when attempting to install SNP HII protocol

HII seems to fail on several systems.  Since it is non-essential,
treat HII problems as non-fatal.

Debugged-by: Curtis Larsen <larsen@dixie.edu>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
[efi] Expand the range of well-known EFI GUIDs in debug messages

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[efi] Provide efi_handle_name() for debugging

Provide a function efi_handle_name() (as a generalisation of
efi_handle_devpath_text()) which tries various methods to produce a
human-readable name for an EFI handle.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[efi] Add ability to dump all openers of a given protocol on a handle

Signed-off-by: Michael Brown <mcb30@ipxe.org>