utils/genrandconfig: disable cramfs images

Fixes build error:

  warning: estimate of required size (upper bound) is 1374MB, but
  maximum image size is 272MB, we might die prematurely
  mkcramfs: filesystem too big

Fixes:
http://autobuild.buildroot.net/results/d47/d47f9b462707dffe1b6665f143701303b04e2adc/

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit af5ccec266dbb7925ac12622f379dacb20087ddd)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

utils/genrandconfig

@@ -512,6 +512,9 @@ def fixup_config(sysinfo, configfile):
         configlines.remove('BR2_TARGET_OPTEE_OS=y\n')
         configlines.remove('BR2_TARGET_OPTEE_OS_PLATFORM=""\n')
 
+    if 'BR2_TARGET_ROOTFS_CRAMFS=y\n' in configlines:
+        configlines.remove('BR2_TARGET_ROOTFS_CRAMFS=y\n')
+
     if 'BR2_TARGET_ROOTFS_EXT2=y\n' in configlines and \
        'BR2_TARGET_ROOTFS_EXT2_SIZE="60M"\n' in configlines:
         configlines.remove('BR2_TARGET_ROOTFS_EXT2_SIZE="60M"\n')