x86/boot/compressed: Simplify IDT/GDT preserve/restore in the EFI thunk

commit 630f337f upstream.

Tweak the asm and remove some redundant instructions. While at it,
fix the associated comment for style and correctness.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221122161017.2426828-9-ardb@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>