libstagefright: refactor Legacy LPA makefile

  - add in msm7x27a
  - remove unused USE_LPA_MODE flag

Change-Id: I9e8d9376e1cfbd37e6457c0fd8e6252848f6b24d
libstagefright: Enable meta mode for 7x27a video encoder

msm7627a family of chipsets supports only one input frame at
one time. camera expects the input frame to be released before
sending another frame. so send one input buffer and available
output bufefrs to video encoder component. Release the input
buffer to camera (to get another frame) after receiving input
frame done callback from video encoder component.

Change-Id: I8fbc911f046ff7e2a3047dd65d8c09ac2d8608e2