arc: Remove obsolete options

arc: Remove obsolete options

Remove the following obsolete options:
- munalign-prob-threshold
- malign-call
- mmixed-code

The ARC's options are marked as obsolete and ignored for backwards
compatibility.

gcc/
2021-06-03  Claudiu Zissulescu  <claziss@synopsys.com>

	* common/config/arc/arc-common.c (arc_option_optimization_table):
	Remove malign-call.
	* config/arc/arc.c (arc_unalign_branch_p): Remove unused function.
	* config/arc/arc.h (TARGET_MIXED_CODE): Remove macro.
	(INDEX_REG_CLASS): Only refer to GENERAL_REGS.
	* config/arc/arc.md (abssi2_mixed): Remove pattern.
	* config/arc/arc.opt (munalign-prob-threshold): Mark it obsolete.
	(malign-call): Likewise.
	(mmixed-code): Likewise.
	* doc/invoke.texi (ARC): Update doc.

Signed-off-by: Claudiu Zissulescu <claziss@synopsys.com>