package/qemu: disable doc generation for host build

- disable doc generation (via sphinx) for host build

Reduces host-qemu build time from (on a system with sphinx installed):

	real    2m5,522s
	user    9m41,292s
	sys     1m9,732s

to:
	real	1m9,183s
	user	8m40,131s
	sys	1m9,533s

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/qemu/qemu.mk

@@ -355,6 +355,7 @@ define HOST_QEMU_CONFIGURE_CMDS
 		--disable-bzip2 \
 		--disable-containers \
 		--disable-curl \
+		--disable-docs \
 		--disable-libssh \
 		--disable-linux-io-uring \
 		--disable-sdl \