isl: fix VA64 support for double and dvecN vertex attributes

isl: fix VA64 support for double and dvecN vertex attributes

We use *64*_PASSTHRU formats to upload vertex attributes of 64 bits
to avoid conversions. From the BDW PRM, Volume 2d, page 586
(VERTEX_ELEMENT_STATE):

     "When SourceElementFormat is set to one of the *64*_PASSTHRU
     formats, 64-bit components are stored in the URB without any
     conversion. In this case, vertex elements must be written as 128
     or 256 bits, with VFCOMP_STORE_0 being used to pad the output
     as required. E.g., if R64_PASSTHRU is used to copy a 64-bit Red
     component into the URB, Component 1 must be specified as
     VFCOMP_STORE_0 (with Components 2,3 set to VFCOMP_NOSTORE)
     in order to output a 128-bit vertex element, or Components 1-3 must
     be specified as VFCOMP_STORE_0 in order to output a 256-bit vertex
     element. Likewise, use of R64G64B64_PASSTHRU requires Component 3
     to be specified as VFCOMP_STORE_0 in order to output a 256-bit vertex
     element."

v2,v3 (Jason):
- Don't delete unused formats.

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>