[MIPS] Apply ASE information for the selected processor

[MIPS] Apply ASE information for the selected processor

GAS does not enable implicit ASEs for most MIPS processors.
The rework of option handling done as part of .module implementation
left the implicit ASE logic broken and default enabled ASEs for
most processors did not get applied.  This patch ensures the ASE
information is carried forward to the point where it is required.

gas/
	* config/tc-mips.c (mips_set_options) <init_ase>: New field.
	(file_mips_opts, mips_opts) <init_ase>: Initialize new field.
	(file_mips_check_options): Propagate initial ASE settings.
	(mips_after_parse_args, parse_code_option): Track the initial
	ASE settings for a CPU.
	(s_mipsset): Restore the initial ASE settings when reverting
	to the default arch.
	* testsuite/gas/mips/elf_mach_p6600.d: New test.
	* testsuite/gas/mips/mips.exp: Run the new test.