efi: Add a media/block driver for EFI block devices

Add a block driver which handles read/write for EFI block devices. This
driver actually already exists ('efi_block') but is not really suitable
for use as a real U-Boot driver:

- The operations do not provide a udevice
- The code is designed for running as part of EFI loader, so uses
    EFI_PRINT() and EFI_CALL().
- The bind method probes the device, which is not permitted
- It uses 'EFI' as its parent device

The new driver is more 'normal', just requiring its platform data be set
up in advance.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

include/efi.h

@@ -414,6 +414,17 @@ struct efi_priv {
 	void *next_hdr;
 };
 
+/*
+ * EFI attributes of the udevice handled by efi_media driver
+ *
+ * @handle: handle of the controller on which this driver is installed
+ * @blkio: block io protocol proxied by this driver
+ */
+struct efi_media_plat {
+	efi_handle_t		handle;
+	struct efi_block_io	*blkio;
+};
+
 /* Base address of the EFI image */
 extern char image_base[];