A format that contains 3 floating point values with a 9-bit mantissa
each and a shared 5-bit exponent.

Maps directly onto the RGB9_E5_EXT format available through the
GL extension EXT_texture_shared_exponent.
Signed-off-by: Sven Hesse <drmccoy@drmccoy.de>
Signed-off-by: Henri Verbeet <hverbeet@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>