arm: Add Prep subcommand support to bootm

Adds prep subcommand to bootm implementation of ARM. When bootm is called
with the subcommand prep the function stops right after ATAGS creation and
before announce_and_cleanup.

This is used in command "cmd_spl export"

Signed-off-by: Simon Schwarz <simonschwarzcor@gmail.com>
Acked-by: Stefano Babic <sbabic@denx.de>
Tested-by: Stefano Babic <sbabic@denx.de>
Signed-off-by: Tom Rini <trini@ti.com>
2 files changed