GXemul supports MIPS Malta but with some limitations.
The most notable problems:

  * PCI-enabled barebox just hangs under GXemul;
  * by default gxemul uses 5Kc processor,
    so we have to force MIPS32R1 processor usage.

To fix these problems the special gxemul-malta_defconfig
is introduced and the board's documentation is updated.

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>