Android.mk: Add a flag to disable libjpeg
Android.mk: Add a flag to disable libjpeg

Do not build jpeg related files if LIBYUV_DISABLE_JPEG  is set to
"yes".

BUG=libyuv:693

Change-Id: If1bc4602fb843ca7b2964844b53553aa0cca551c
Reviewed-on: https://chromium-review.googlesource.com/455475
Reviewed-by: Frank Barchard <52415189a3f67d375195cbbb6fdb1f1759498e57@google.com>
Commit-Queue: Vignesh Venkatasubramanian <32adfcbcff25ad7c4328b41fc62b418a28ad0235@google.com>

lemenkov/libyuv,lemenkov/libyuv,lemenkov/libyuv,lemenkov/libyuv