[amdgcn] Update lower bounds for the number of registers in non-leaf kernels

[amdgcn] Update lower bounds for the number of registers in non-leaf kernels

Reduce the lower limits on the number of registers requested by non-leaf
kernels to help improve CU occupancy.

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

	gcc/
	* config/gcn/gcn.c (MAX_NORMAL_SGPR_COUNT, MAX_NORMAL_VGPR_COUNT): New.
	(gcn_conditional_register_usage): Use constants in place of hard-coded
	values.
	(gcn_hsa_declare_function_name): Set lower bound for number of
	SGPRs/VGPRs in non-leaf kernels to MAX_NORMAL_SGPR_COUNT and
	MAX_NORMAL_VGPR_COUNT.

From-SVN: r278305