glsl/linker: dvec3/dvec4 consume twice input vertex attributes

glsl/linker: dvec3/dvec4 consume twice input vertex attributes

From the GL 4.5 core spec, section 11.1.1 (Vertex Attributes):

"A program with more than the value of MAX_VERTEX_ATTRIBS
active attribute variables may fail to link, unless
device-dependent optimizations are able to make the program
fit within available hardware resources. For the purposes
of this test, attribute variables of the type dvec3, dvec4,
dmat2x3, dmat2x4, dmat3, dmat3x4, dmat4x3, and dmat4 may
count as consuming twice as many attributes as equivalent
single-precision types. While these types use the same number
of generic attributes as their single-precision equivalents,
implementations are permitted to consume two single-precision
vectors of internal storage for each three- or four-component
double-precision vector."

This commits makes dvec3, dvec4, dmat2x3, dmat2x4, dmat3, dmat3x4,
dmat4x3 and dmat4 consume twice as many attributes as equivalent
single-precision types.

v3: count doubles as consuming two attributes (Dave Airlie)
v4: make reference to spec (Michael Schellenberger Costa)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Antia Puentes <apuentes@igalia.com>
Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>