Add and consistently use PLANE_TYPE.

Change the macros PLANE_TYPE_{Y_NO_DC,Y2,UV,Y_WITH_DC} to a typed enum,
and use this typed enum consistently across all places where relevant.
In places where the type is implied (e.g. in functions that only handle
second order planes or chroma planes), remove it as a function argument
and instead hardcode the proper enum in the code directly.

Change-Id: I93652b4a36aa43163d49c732b0bf5c4442738c47