Increase the size of super.img for Goldfish

Current super image for GF is almost full in sdk_gphone_x86_arm
product, and not big enough to include CSI for mixed configuration,
which is a bit bigger than the system image of sdk_gphone_x86_arm.

Bug: 174442566
Test: $ lunch aosp_x86_arm-userdebug; m
      $ ls -l $OUT/super.img	# make sure it's 4 GB
Change-Id: Ia2473231c8490995a10700cbd6e0f82598a5e078