boot/efi: factor out generic mmu functions

This change moves the common functions related to EFI memory map
to arch/generic for arm, arm64, x86.

riscv64 and x86_64 shall be handled separately as they use some
more architecture-specific logic:
* riscv64 needs special treatment for the M-mode resident code
located at 0x80000000 which is reported as available in the
EFI memory map provided by u-boot.
* x86_64 has a slightly different logic for building the
memory regions list so some additional rework and testing will be
needed before it can be unified with the generic mmu functions.

Change-Id: I430c84dfc693c5b6f04c170dec8ffb1db2c2ace1
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5694
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

boot/efi/x86: move bootGDTDescriptor to local variable

Global variable gBootGDTDescriptor is used only in function arch_start_kernel()
so we can convert it to a local variable.

Change-Id: I8b6ad2c0903364bdcdcc1039aea6c9c09253fe09
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5663
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: David Karoly <karolyd577@gmail.com>

boot/efi/x86: move bootGDT local variable

Global variable gBootGDT is used only in function arch_mmu_init_gdt()
so we can convert it to a local variable.

Change-Id: I06174dcd6df4b7bd5136a7e2fabafdc3273f03d3
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5662
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Fredrik Holmqvist <fredrik.holmqvist@gmail.com>

boot/efi/x86: implement MMU initialization and jump to kernel

Change-Id: Ie42c69f3851acae3a8184aa97ab2dd01c9485f46
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4850
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

boot/efi: add stubs for x86

Change-Id: I8d3dfa7cc07679a8b024df24f7cddb3a5bcec02c
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4747
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>