[amdgcn] Reinitialize registers for every function

[amdgcn] Reinitialize registers for every function

gcn_conditional_register_usage needs to be called for every function
to set the fixed registers depending on the kernel args currently
requested.

2019-11-15  Kwok Cheung Yeung  <kcy@codesourcery.com>

	gcc/
	* config/gcn/gcn.c (gcn_init_cumulative_args): Call reinit_regs.

From-SVN: r278299