Merge vim and vimrc Android.mk in a single file

Add also a fallback for $VIMRUNTIME env var,
if not set, syntax.vim could be not loaded

Its easier to read, and allow custom rules on the
first prebuilt, if required.

Add also markdown and syntax.pod, to read manuals
and use the default colored format in build process
for runtime files.

Install: /cm11/out/target/product/bacon/...

Change-Id: I45f8af834f2bee28962d120f94580fc47193adc4