generic: improve kexec support of MIPS.

- Allow --command-line parameters of kexec-tools be parsed and used by
   the kernel.
 - For malta machine, mark kernel code and kernel data segments as
   "System RAM" instead of "reserved" in /proc/iomem, otherwise
   kexec-tools will complain that program segments in ELF kernel file
   are invalid.

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

SVN-Revision: 44429