cmd_bootm.c: Add 'booti' for ARM64 Linux kernel Images

The default format for arm64 Linux kernels is the "Image" format,
described in Documentation/arm64/booting.txt.  This, along with an
optional gzip compression on top is all that is generated by default.
The Image format has a magic number within the header for verification,
a text_offset where the Image must be run from, an image_size that
includes the BSS and reserved fields.

This does not support automatic detection of a gzip compressed image.

Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/README b/README
index 517b0b4..0a0f528 100644
--- a/README
+++ b/README
@@ -959,6 +959,7 @@
 		CONFIG_CMD_BMP		* BMP support
 		CONFIG_CMD_BSP		* Board specific commands
 		CONFIG_CMD_BOOTD	  bootd
+		CONFIG_CMD_BOOTI	* ARM64 Linux kernel Image support
 		CONFIG_CMD_CACHE	* icache, dcache
 		CONFIG_CMD_CLK   	* clock command support
 		CONFIG_CMD_CONSOLE	  coninfo