ac: add ac_shader_abi.h in distcheck

ac: add ac_shader_abi.h in distcheck

Fixes:

  CXXLD    addrlib/libamdgpu_addrlib.la
ar: `u' modifier ignored since `D' is the default (see `U')
../../../../src/amd/common/ac_nir_to_llvm.c:33:27: fatal error:
ac_shader_abi.h: No such file or directory
 #include "ac_shader_abi.h"
                           ^
compilation terminated.
Makefile:985: recipe for target
'common/common_libamd_common_la-ac_nir_to_llvm.lo' failed

When running `make distcheck`

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>