efi_loader: Add bounce buffer support

Some hardware that is supported by U-Boot can not handle DMA above 32bits.
For these systems, we need to come up with a way to expose the disk interface
in a safe way.

This patch implements EFI specific bounce buffers. For non-EFI cases, this
apparently was no issue so far, since we can just define our environment
variables conveniently.

Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/include/efi_loader.h b/include/efi_loader.h
index 8005454..b1ca4ba 100644
--- a/include/efi_loader.h
+++ b/include/efi_loader.h
@@ -139,6 +139,11 @@
 /* Called by board init to initialize the EFI memory map */
 int efi_memory_init(void);
 
+#ifdef CONFIG_EFI_LOADER_BOUNCE_BUFFER
+extern void *efi_bounce_buffer;
+#define EFI_LOADER_BOUNCE_BUFFER_SIZE (64 * 1024 * 1024)
+#endif
+
 /* Convert strings from normal C strings to uEFI strings */
 static inline void ascii2unicode(u16 *unicode, char *ascii)
 {