drm/radeon: change si_default_state table from global to static

Smatch reports these issues
si_blit_shaders.c:31:11: warning: symbol 'si_default_state'
  was not declared. Should it be static?
si_blit_shaders.c:253:11: warning: symbol 'si_default_size'
  was not declared. Should it be static?

Both symbols are only used in si.c.  Single file symbols
should be static.  So move the definition of
si_default_state and si_default_size to si_blit_shader.h
and change their storage-class-specifier to static.

Remove unneeded si_blit_shader.c

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>