loongarch: efi: enable generic EFI compressed boot

Wire up the generic EFI zboot support for LoongArch64

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

efi/loongarch: Add efistub booting support

This patch adds efistub booting support, which is the standard UEFI boot
protocol for LoongArch to use.

We use generic efistub, which means we can pass boot information (i.e.,
system table, memory map, kernel command line, initrd) via a light FDT
and drop a lot of non-standard code.

We use a flat mapping to map the efi runtime in the kernel's address
space. In efi, VA = PA; in kernel, VA = PA + PAGE_OFFSET. As a result,
flat mapping is not identity mapping, SetVirtualAddressMap() is still
needed for the efi runtime.

Tested-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
[ardb: change fpic to fpie as suggested by Xi Ruoyao]
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

LoongArch: Add build infrastructure

Add Kbuild, Makefile, Kconfig and link script for LoongArch build
infrastructure.

Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>