LoongArch: Enable general EFI poweroff method

LoongArch: Enable general EFI poweroff method

efi_shutdown_init() can register a general sys_off handler named
efi_power_off(). Enable this by providing efi_poweroff_required(),
like arm and x86. Since EFI poweroff is also supported on LoongArch,
and the enablement makes the poweroff function usable for hardwares
which lack ACPI S5.

We prefer ACPI poweroff rather than EFI poweroff (like x86), so we only
require EFI poweroff if acpi_gbl_reduced_hardware or acpi_no_s5 is true.

Cc: stable@vger.kernel.org
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Miao Wang <shankerwangmiao@gmail.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>