Remove custom bcm21553 HAL pixel formats

* Use default value for HAL_PIXEL_FORMAT_YV12 (will be aligned in
  graphics driver)
* Move HAL_PIXEL_FORMAT_YCbCr_420_SP and HAL_PIXEL_FORMAT_YCbCr_420_P to
  private gralloc header.

Change-Id: I6565fab8bc8ffb0e31074e9199a9141800b1222a