board/qemu/mips*-malta: switch from IDE disk to SCSI disk

A following patch will switch to the kernel 5.15 for all qemu
defconfigs but the IDE support (used by mips malta) has been
removed from the Linux kernel since 5.14 release [1].

Enable the SCSI support and update the kernel command line.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b7fb14d3ac63117e0e8beabe75f4ea52051fbe3a



Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>