i965: Bump MAX_3D_TEXTURE_SIZE to 2048.

i965: Bump MAX_3D_TEXTURE_SIZE to 2048.

It's highly unlikely that there will be enough memory in the system to
allocate enough space for this, but we should still expose the hardware
limit.  It's what the Intel Windows driver does, and it seems most other
vendors do likewise.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=74130
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>