utils/genrandconfig: handle BR2_LINUX_KERNEL_IMAGE_TARGET_CUSTOM=y

When BR2_LINUX_KERNEL_IMAGE_TARGET_CUSTOM=y,
BR2_LINUX_KERNEL_IMAGE_TARGET_NAME is supposed to be non-empty. But in
the context of genraconfig, we don't know to what value
BR2_LINUX_KERNEL_IMAGE_TARGET_NAME can be set, so let's avoid cases
where BR2_LINUX_KERNEL_IMAGE_TARGET_CUSTOM=y. By dropping this option,
kconfig will revert back to the default image format for the selected
architecture.

Fixes:

  http://autobuild.buildroot.net/results/1d104a051c83bb31e98565369a2ec7badfa21eca/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit b07d21ab984d10cbabeb186fbd47d446e027c03b)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

utils/genrandconfig

@@ -241,6 +241,10 @@ async def fixup_config(sysinfo, configfile):
             configlines.remove('BR2_LINUX_KERNEL_SIMPLEIMAGE=y\n')
             configlines.append('BR2_LINUX_KERNEL_VMLINUX=y\n')
 
+    if 'BR2_LINUX_KERNEL=y\n' in configlines and \
+       'BR2_LINUX_KERNEL_IMAGE_TARGET_CUSTOM=y\n' in configlines:
+        configlines.remove('BR2_LINUX_KERNEL_IMAGE_TARGET_CUSTOM=y')
+
     if 'BR2_LINUX_KERNEL_EXT_AUFS=y\n' in configlines and \
        'BR2_LINUX_KERNEL_EXT_AUFS_VERSION=""\n' in configlines:
         configlines.remove('BR2_LINUX_KERNEL_EXT_AUFS=y\n')