system_dlkm and vendor_dlkm can be ext4 or erofs images
as these are supported read only filesystem in platform
builds.

Add an option to choose between ext4/erofs for these
partitions for the kernel's development only images to
match patform choices with ext4 as the default if choice
is not provided.

Choice will be passed as environemental variables to build_utils.sh:
SYSTEM_DLKM_FS_TYPE=["ext4" | "erofs"] for build_system_dlkm_image
VENDOR_DLKM_FS_TYPE=["ext4" | "erofs"] for build_vendor_dlkm_image

Bug: 261617174
Bug: 232430739
Test: TH
Change-Id: I4a37e9d0116bb4b2f38fc119011a441d7c73e9f7
Signed-off-by: Ramji Jiyani <ramjiyani@google.com>