i965: Explicitly maintain a count of SO_DECL structures emitted.

i965: Explicitly maintain a count of SO_DECL structures emitted.

Currently, we emit one SO_DECL structure per output, so we use the index
in the Outputs[] array as the index into the so_decl[] array as well.

In order to support the fake "gl_SkipComponents[1234]" varyings from
ARB_transform_feedback3, we'll need to emit SO_DECLs to fill in the
holes between successive outputs.  This means we'll likely emit more
SO_DECLs than there are outputs, so we need to count it explicitly.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>