graphics: Add directives for compatibility with older EGL blobs

- Define MISSING_EGL_EXTERNAL_IMAGE for EGL libraries without
  GL_OES_GLES_image_external
- Define MISSING_GRALLOC_BUFFERS for gralloc HALS without the
  0x800 (USAGE_HW_COMPOSER) usage
- Define MISSING_EGL_PIXEL_FORMAT_YV12 for libraries who don't
  recognize the Android YV12 colorspace
- Define FORCE_EGL_CONFIG=<value> for blobs which mis-identify the
  usable EGL configuration (pick the value from a CM7 log)

A typical GB library set will need
COMMON_GLOBAL_CFLAGS += -DMISSING_EGL_EXTERNAL_IMAGE -DMISSING_EGL_PIXEL_FORMAT_YV12 -DMISSING_GRALLOC_BUFFERS

Change-Id: I85ae813c604d3d2fc41a291c9cb13d1ecd35368f