efi: support booting with kexec handover (KHO)

efi: support booting with kexec handover (KHO)

When KHO (Kexec HandOver) is enabled, it sets up scratch memory regions
early during device tree scanning.  After kexec, the new kernel
exclusively uses this region for memory allocations during boot up to the
initialization of the page allocator

However, when booting with EFI, EFI's reserve_regions() uses
memblock_remove(0, PHYS_ADDR_MAX) to clear all memory regions before
rebuilding them from EFI data.  This destroys KHO scratch regions and
their flags, thus causing a kernel panic, as there are no scratch memory
regions.

Instead of wholesale removal, iterate through memory regions and only
remove non-KHO ones.  This preserves KHO scratch regions, which are good
known memory, while still allowing EFI to rebuild its memory map.

Link: https://lkml.kernel.org/r/b34da9fd50c89644cd4204136cfa6f5533445c56.1755721529.git.epetron@amazon.de
Signed-off-by: Evangelos Petrongonas <epetron@amazon.de>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>