efi_loader: expose symbols to be used by the EFI network stack

efi_loader: expose symbols to be used by the EFI network stack

The following symbols are exposed:
	- efi_reinstall_protocol_interface
		This is done so that the device path protocol interface
		of the network device can be changed internally by u-boot
		when a new bootfile gets downloaded.
	- eth_set_dev
		To support multiple network udevices
	- efi_close_event
		This comes in preparation to support unregistering
		an EFI network device from the EFI network stack when
		the underlying U-boot device gets removed
	- efi_[dis]connect_controller
		The EFI network driver uses ConnectController to add a
		NIC to the EFI network stack.
	- efi_uninstall_protocol_interface
		connect_controler for the efi network driver can install
		protocols, which need to be uninstalled in disconnect_controller
	- EFI_SIMPLE_NETWORK_PROTOCOL_GUID

Signed-off-by: Adriano Cordova <adriano.cordova@canonical.com>