dri: Introduce new flags in __DRI_ATTRIB_RENDER_TYPE

dri: Introduce new flags in __DRI_ATTRIB_RENDER_TYPE

Mark __DRI_ATTRIB_FLOAT_MODE as deprecated, and introduce new flags to
__DRI_ATTRIB_RENDER_TYPE for float modes.  Both signed float
(fbconfig_float) and unsigned (packed_float) are introduced. The old
attribute should be set for both float modes.

v2 (idr): Require that the render mode from the DRI attributes matches the
render mode of the config exactly.  This is the behavior of the old code.

Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>