cmd_bootm.c: Change interpretation of standalone image parameters.

Current code uses the second argument to bootm for standalone images to
override the load address specified in the image instead of passing all
parameters as is to the application.  This behaviour is not documented
and not in line with how the go command works for standalone applications,
so we simply drop it.

Signed-off-by: Detlev Zundel <dzu@denx.de>