LoongArch: Add a missing call to efi_esrt_init()

ESRT (EFI System Resource Table) is needed for UEFI's "Capsule Update"
feature. But ESRT initialization is missing on LoongArch now, so add a
call to efi_esrt_init() at the end of efi_init().

Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>