fedora-arm-minimal: increase root partition size

The image creation currently silently fails on Fedora 33 because the
kernel scriptlet is unable to create the initramfs:

  cp: error writing '/var/tmp/dracut.SqTiPj/initramfs/lib/libbrotlicommon.so.1.0.7': No space left on device
  dracut-install: ERROR: failed to install '/lib/libbrotlicommon.so.1' for '/var/tmp/dracut.SqTiPj/initramfs/usr/sbin/rngd'
  ...

I'm not entirely sure how much space is actually needed. Hopefully not
more than 100M though.

fedora-arm-minimal.ks

@@ -1,7 +1,7 @@
 %include fedora-arm-base.ks
 %include fedora-minimal-common.ks
 
-part / --size=1400 --fstype ext4
+part / --size=1500 --fstype ext4
 
 %packages
 -xkeyboard-config