qemuarmv7: add KMACHINE config

Otherwise kernel build fails with error: Could not locate BSP definition
for qemuarmv7/standard and no defconfig was provided.

Change-Id: Ibca0b104b34e70cc22b51f7e22015b55da25cb1b
Reviewed-by: Sami Nurmenniemi <sami.nurmenniemi@qt.io>

meta-boot2qt-distro/conf/machine/qemuarmv7.conf

@@ -6,3 +6,5 @@ DEFAULTTUNE = "armv7athf-neon"
 
 require conf/machine/include/qemu.inc
 require conf/machine/include/arm/arch-armv7a.inc
+
+KMACHINE = "qemuarm"