i965/gen8/cs: Gen8 requires 64 byte alignment for push constant data

i965/gen8/cs: Gen8 requires 64 byte alignment for push constant data

The BDW PRM Vol2a: Command Reference: Instructions, section MEDIA_CURBE_LOAD,
says that 'CURBE Total Data Length' and 'CURBE Data Start Address' are
64-byte aligned. This is different from previous gens, that were 32-byte
aligned.

v2 (Jordan):
  - CURBE Data Start Address is also 64-byte aligned.
    - The call to brw_state_batch should also use 64-byte alignment.
      - Improve PRM reference.

v3:
 * New patch from Jordan. Always align base and size to 64 bytes.

Fixes the following SSBO CTS tests on BDW:
ES31-CTS.shader_storage_buffer_object.basic-atomic-case1-cs
ES31-CTS.shader_storage_buffer_object.basic-operations-case1-cs
ES31-CTS.shader_storage_buffer_object.basic-operations-case2-cs
ES31-CTS.shader_storage_buffer_object.basic-stdLayout_UBO_SSBO-case2-cs
ES31-CTS.shader_storage_buffer_object.advanced-write-fragment-cs
ES31-CTS.shader_storage_buffer_object.advanced-indirectAddressing-case2-cs
ES31-CTS.shader_storage_buffer_object.advanced-matrix-cs

And many other CS CTS tests as reported by Marta Lofstedt.

(Commit message is from Iago, but in v3, code is from Jordan.)

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Tested-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>