Reimplement LEAF_REG_REMAP macro for the SPARC

Reimplement LEAF_REG_REMAP macro for the SPARC

The current implementation as an array of chars is indeed a bit awkward
so this reimplements it as a function taking and returning an int.

gcc/
	* config/sparc/sparc-protos.h (order_regs_for_local_alloc): Rename
	to...
	(sparc_order_regs_for_local_alloc): ...this.
	(sparc_leaf_reg_remap): Declare.
	* config/sparc/sparc.h (ADJUST_REG_ALLOC_ORDER): Adjust.
	(LEAF_REG_REMAP): Reimplement as call to sparc_leaf_reg_remap.
	* config/sparc/sparc.c (leaf_reg_remap): Delete.
	(order_regs_for_local_alloc): Rename to...
	(sparc_order_regs_for_local_alloc): ...this.
	(sparc_leaf_reg_remap): New function.
	(sparc_conditional_register_usage): Do not modify leaf_reg_remap.