mesa: restrict use of GL_ABGR_EXT format to allowed data types

GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV,
GL_UNSIGNED_INT_10_10_10_2, GL_UNSIGNED_INT_2_10_10_10_REV data types
are not explicitly allowed to work with GL_ABGR_EXT format neither
in GL nor GL_EXT_abgr specs.

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>