scripts/qemustart: update malta to use MIPS64 R2 cpu

Explicitly set the QEMU cpu type and support the MIPS R2 ISA, for both
64-bit and 32-bit targets. The later previously supported MIPS R2 by
implicit default.

This is needed after commit 9360869 ("malta: update MIPS64 ISA to R2"),
otherwise booting malta images with scripts/qemustart will hang.

Signed-off-by: Tony Ambardar <itugrok@yahoo.com>

scripts/qemustart

@@ -212,6 +212,7 @@ start_qemu_malta() {
 	local is64
 	local isel
 	local qemu_exe
+	local cpu
 	local rootfs="$o_rootfs"
 	local kernel="$o_kernel"
 	local mach="${o_mach:-malta}"
@@ -220,6 +221,7 @@ start_qemu_malta() {
 	is64="$(echo $o_subtarget | grep -o 64)"
 	[ "$(echo "$o_subtarget" | grep -o '^..')" = "le" ] && isel="el"
 	qemu_exe="qemu-system-mips$is64$isel"
+	[ -n "$is64" ] && cpu="MIPS64R2-generic" || cpu="24Kc"
 
 	[ -n "$kernel" ] || kernel="$o_bindir/openwrt-malta-${o_subtarget%-*}-vmlinux-initramfs.elf"
 
@@ -243,7 +245,7 @@ start_qemu_malta() {
 		)
 	}
 
-	"$qemu_exe" -machine "$mach" -nographic \
+	"$qemu_exe" -machine "$mach" -cpu "$cpu" -nographic \
 		-kernel "$kernel" \
 		"${o_qemu_extra[@]}"
 }