gpu: store block sizes only in ppcg_kernel

gpu: store block sizes only in ppcg_kernel

Since 561c8ae (use isl for CUDA code generation, Tue Jul 31 21:00:26 2012 +0200)
we keep a copy of the block sizes in gpu_gen in ppcg_kernel so that we can
use them during printing.  Since c7179a0 (gpu.c: compute effective block size,
Fri Apr 12 13:41:10 2013 +0200), the block sizes in gpu_gen represent
the user specified sizes, while the block sizes in ppcg_kernel represent
the effective sizes.
There is, however, no need to keep the user specified sizes once
the effective sizes have been computed.  Moreover, there is no need
to keep the block sizes in gpu_gen.  Only keep them in ppcg_kernel,
where they now represent the user specified sizes until the effective
sizes have been computed.

Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>