MIPS: Loongson: Add UEFI-like firmware interface (LEFI) support

The new UEFI-like firmware interface (LEFI, i.e. Loongson Unified
Firmware Interface) has 3 advantages:

1, Firmware export a physical memory map which is similar to X86's
   E820 map, so prom_init_memory() will be more elegant that #ifdef
   clauses can be removed.
2, Firmware export a pci irq routing table, we no longer need pci
   irq routing fixup in kernel's code.
3, Firmware has a built-in vga bios, and its address is exported,
   the linux kernel no longer need an embedded blob.

With the LEFI interface, Loongson-3A/2G and all their successors can use
a unified kernel. All Loongson-based machines support this new interface
except 2E/2F series.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Hongliang Tao <taohl@lemote.com>
Signed-off-by: Hua Yan <yanh@lemote.com>
Tested-by: Alex Smith <alex.smith@imgtec.com>
Reviewed-by: Alex Smith <alex.smith@imgtec.com>
Cc: John Crispin <john@phrozen.org>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: linux-mips@linux-mips.org
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/6632


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>