When allocating EFI memory pages the size in bytes has to be converted to
pages.

Provide a macro efi_size_in_pages() for this conversion.
Use it in the EFI subsystem and correct related comments.
Signed-off-by: NHeinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: NAlexander Graf <agraf@suse.de>