package/qemu: fix armeb build

Fix the following armeb build failure raised since at least version
6.2.0:

ERROR: Unknown target name 'armeb-softmmu'

Fixes:
 - http://autobuild.buildroot.org/results/dbd1417fb638ad41e9f23941141bbeb9c999fb05
 - http://autobuild.buildroot.org/results/a6f97308aa2e634ed3d5b80b33b4663aa16c4693

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/qemu/qemu.mk

@@ -277,6 +277,9 @@ HOST_QEMU_DEPENDENCIES = host-meson host-pkgconf host-zlib host-libglib2 host-pi
 #       xtensa          xtensa
 
 HOST_QEMU_ARCH = $(ARCH)
+ifeq ($(HOST_QEMU_ARCH),armeb)
+HOST_QEMU_SYS_ARCH = arm
+endif
 ifeq ($(HOST_QEMU_ARCH),i486)
 HOST_QEMU_ARCH = i386
 endif