cmd: load: add load command for memory mapped

cp.b is used a lot as a way to load binaries to memory and execute
them, however we may need to integrate this with the efi subsystem to
set it up as a bootdev.

So, introduce a loadm command that will be consistent with the other
loadX commands and will call the efi API's.

ex: loadm $kernel_addr $kernel_addr_r $kernel_size

with this a kernel with CONFIG_EFI_STUB enabled will be loaded and
then subsequently booted with bootefi command.

Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

doc/usage/cmd/loadm.rst

@@ -0,0 +1,49 @@
+.. SPDX-License-Identifier: GPL-2.0+:
+
+loadm command
+=============
+
+Synopsis
+--------
+
+::
+
+    loadm <src_addr> <dst_addr> <len>
+
+Description
+-----------
+
+The loadm command is used to copy memory content from source address
+to destination address and, if efi is enabled, will setup a "Mem" efi
+boot device.
+
+The number of transferred bytes must be set by bytes parameter
+
+src_addr
+    start address of the memory location to be loaded
+
+dst_addr
+    destination address of the byte stream to be loaded
+
+len
+    number of bytes to be copied in hexadecimal. Can not be 0 (zero).
+
+Example
+-------
+
+::
+
+    => loadm ${kernel_addr} ${kernel_addr_r} ${kernel_size}
+    loaded bin to memory: size: 12582912
+
+Configuration
+-------------
+
+The command is only available if CONFIG_CMD_LOADM=y.
+
+Return value
+------------
+
+The return value $? is set 0 (true) if the loading is succefull, and
+is set to 1 (false) in case of error.
+