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>
diff --git a/configs/sandbox64_defconfig b/configs/sandbox64_defconfig
index 9d72e39..46a9b16 100644
--- a/configs/sandbox64_defconfig
+++ b/configs/sandbox64_defconfig
@@ -47,6 +47,7 @@
 CONFIG_CMD_GPT_RENAME=y
 CONFIG_CMD_IDE=y
 CONFIG_CMD_I2C=y
+CONFIG_CMD_LOADM=y
 CONFIG_CMD_OSD=y
 CONFIG_CMD_PCI=y
 CONFIG_CMD_READ=y