Support building EROFS for GSI targets

The EROFS is planned to replace the ext4 as the file system format
of readonly partitions. This patch is enabling the ability to
build GSI with EROFS. The usage is

  $ GSI_FILE_SYSTEM_TYPE=erofs make -j

Bug: 227552340
Test: lunch gsi_arm64-user; GSI_FILE_SYSTEM_TYPE=erofs make -j
Test: Verify the file system format of system.img
Change-Id: Ie815002c677d099c4db0ab7ca22db16ac6123659