MIPS: Malta: enable Cirrus FB console

While most users of a physical Malta board are using the serial port
as the console, a lot of QEMU users would prefer to interact with a
graphical console. Enable the Cirrus FB support in the Malta default
configuration to make that possible. Note that the default console will
still be the serial port, users have to pass "console=tty0" to the
kernel to use the Cirrus FB.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2001/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>