Add early_platform_init_buffer() support and update the
early platform driver code to allow passing parameters
to the driver on the kernel command line.

early_platform_init_buffer() simply allows early platform
drivers to provide a pointer and length to a memory area
where the remaining part of the kernel command line option
will be stored.

Needed to pass baud rate and other serial port options
to the reworked early serial console code on SuperH.
Signed-off-by: NMagnus Damm <damm@opensource.se>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>