loongarch: Change the UEFI loading mode to loongarch

loongarch: Change the UEFI loading mode to loongarch

The UEFI loading mode in loongarch is very different
from that in other architectures:loongarch's UEFI code
is in rom, while other architectures' UEFI code is in flash.

loongarch UEFI can be loaded as follows:
-machine virt,pflash=pflash0-format
-bios ./QEMU_EFI.fd

Other architectures load UEFI using the following methods:
-machine virt,pflash0=pflash0-format,pflash1=pflash1-format

loongarch's UEFI loading method makes qemu and libvirt incompatible
when using NVRAM, and the cost of loongarch's current loading method
far outweighs the benefits, so we decided to use the same UEFI loading
scheme as other architectures.

Cc: Andrea Bolognani <abologna@redhat.com>
Cc: maobibo@loongson.cn
Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
Cc: Song Gao <gaosong@loongson.cn>
Cc: zhaotianrui@loongson.cn
Signed-off-by: Xianglai Li <lixianglai@loongson.cn>
Tested-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Message-Id: <0bd892aa9b88e0f4cc904cb70efd0251fc1cde29.1708336919.git.lixianglai@loongson.cn>
Signed-off-by: Song Gao <gaosong@loongson.cn>