i965/gen8: Fix vertex attrib upload for dvec3/4 shader inputs

i965/gen8: Fix vertex attrib upload for dvec3/4 shader inputs

The emission of vertex attributes corresponding to dvec3 and dvec4
vertex shader input variables was not correct when the <size> passed
to the VertexAttribL* commands was <= 2.

This was because we were using the vertex array size when emitting vertices
to decide if we uploaded a 64-bit floating point attribute as 1 slot (128-bits)
for sizes 1 and 2, or 2 slots (256-bits) for sizes 3 and 4. This caused problems
when mapping the input variables to registers because, for deciding which
registers contain the values uploaded for a certain variable, we use the size
and type given to the variable in the shader, so we will be assigning 256-bits
to dvec3/4 variables, even if we only uploaded 128-bits for them, which happened
when the vertex array size was <= 2.

The patch uses the shader information to only emit as 128-bits those 64-bit floating
point variables that were declared as double or dvec2 in the vertex shader. Dvec3 and
dvec4 variables will be always uploaded as 256-bits, independently of the <size> given
to the VertexAttribL* command.

From the ARB_vertex_attrib_64bit specification:

   "For the 64-bit double precision types listed in Table X.1, no default
    attribute values are provided if the values of the vertex attribute variable
    are specified with fewer components than required for the attribute
    variable. For example, the fourth component of a variable of type dvec4
    will be undefined if specified using VertexAttribL3dv or using a vertex
    array specified with VertexAttribLPointer and a size of three."

We are filling these unspecified components with zeros, which coincidentally is
also what the GL44-CTS.vertex_attrib_binding.basic-inputL-case1 expects.

v2: Do not use bitcount (Kenneth Graunke)

Fixes: GL44-CTS.vertex_attrib_binding.basic-inputL-case1 test
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97287
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>