rs5000: Delete all specific asm_cpu_* and ASM_CPU_*_SPEC

rs5000: Delete all specific asm_cpu_* and ASM_CPU_*_SPEC

Now that e.g. ASM_CPU_POWER5_SPEC is always "-mpower5" it is clearer and
easier to just write that directly.

	* config/rs6000/driver-rs6000.c (asm_names): Adjust the entries for
	power5 .. power9 to remove indirection.
	* config/rs6000/rs6000.h (ASM_CPU_POWER5_SPEC, ASM_CPU_POWER6_SPEC,
	ASM_CPU_POWER7_SPEC, ASM_CPU_POWER8_SPEC, ASM_CPU_POWER9_SPEC,
	ASM_CPU_476_SPEC): Delete.
	(ASM_CPU_SPEC): Adjust.
	(EXTRA_SPECS): Delete asm_cpu_power5, asm_cpu_power6, asm_cpu_power7,
	asm_cpu_power8, asm_cpu_power9, asm_cpu_476.

From-SVN: r264704