core: allow specifying building ramdisk(s) with lzma

* Add a flag that specifies which ramdisk(s) to compress with lzma
* If not specified, fall back to gzip
* Example: LZMA_RAMDISK_TARGETS := boot,recovery

Change-Id: I9cce4da90343fb6dfb7039863649e37d78262726

Force bsdiff for recovery_from_boot.p if not using GZIP

imgdiff expects a ramdisk to use GZIP, which is causing a chunk
size issue if recovery is using LZMA

Change-Id: I3194b4faed25a298fe23b4e24b6dea2885bafda8

Change-Id: I9cce4da90343fb6dfb7039863649e37d78262726