[scripts] make sure all the do-qemu* scripts exec qemu as the last line

This helps a wrapper script test for proper exit.

scripts/do-qemuarm

@@ -192,4 +192,4 @@ fi
 set -e
 "$DIR"/make-parallel $MAKE_VARS PROJECT="$PROJECT"
 echo "$SUDO" $QEMU $ARGS "$@"
-$SUDO $QEMU $ARGS "$@"
+exec $SUDO $QEMU $ARGS "$@"

scripts/do-qemum4

@@ -57,4 +57,4 @@ fi
 
 $DIR/make-parallel $MAKE_VARS $PROJECT &&
 echo $QEMUM4 $ARGS $@ &&
-$QEMUM4 $ARGS $@
+exec $QEMUM4 $ARGS $@

scripts/do-qemum68k

@@ -8,4 +8,4 @@ set -x
 PROJECT=qemu-virt-m68k-test
 
 $DIR/make-parallel $PROJECT
-qemu-system-m68k -machine virt -cpu m68040 -kernel build-${PROJECT}/lk.elf -nographic $@
+exec qemu-system-m68k -machine virt -cpu m68040 -kernel build-${PROJECT}/lk.elf -nographic $@

scripts/do-qemumicroblaze

@@ -6,4 +6,4 @@ set -e
 set -x
 
 $DIR/make-parallel qemu-microblaze-test
-qemu-system-microblaze -kernel build-qemu-microblaze-test/lk.elf -nographic $@
+exec qemu-system-microblaze -kernel build-qemu-microblaze-test/lk.elf -nographic $@

scripts/do-qemumips

@@ -6,4 +6,4 @@ set -e
 set -x
 
 $DIR/make-parallel qemu-mips-test
-qemu-system-mips -machine mips -cpu M14K -kernel build-qemu-mips-test/lk.elf -nographic $@
+exec qemu-system-mips -machine mips -cpu M14K -kernel build-qemu-mips-test/lk.elf -nographic $@

scripts/do-qemuriscv

@@ -168,4 +168,4 @@ fi
 
 $DIR/make-parallel $MAKE_VARS $PROJECT &&
 echo $SUDO $QEMU $ARGS $@ &&
-$SUDO $QEMU $ARGS $@
+exec $SUDO $QEMU $ARGS $@

scripts/do-qemux86

@@ -140,5 +140,4 @@ fi
 
 $DIR/make-parallel $MAKE_VARS $PROJECT &&
 echo $SUDO $QEMU $ARGS $@ &&
-$SUDO $QEMU $ARGS $@
-
+exec $SUDO $QEMU $ARGS $@