bootm: Create a struct for argument information

bootm: Create a struct for argument information

Some OS functions require the arguments to the 'bootm' command. This is
inconvenient for two reasons.

Firstly, there may not be any actual command, if CMDLINE is not enabled
and programmatic boot is being used.

Secondly, most functions don't require the arguments, so it is
inefficient to pass them when not needed. For example it increases code
size.

Create a new struct which holds the arguments, which can be used if
needed.

Add the images pointer as well, since this is commonly needed.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>