[Patch, ARM] Relax the restrictions on REG_SP under Thumb mode on ARMv8-A

[Patch, ARM] Relax the restrictions on REG_SP under Thumb mode on ARMv8-A

  For Thumb mode, since ARMv8-A, REG_SP is allowed in most of the places in
Rd/Rt/Rt2 etc while it was disallowed before ARMv8-A, and was rejected through
the "reject_bad_reg" macro and several scattered checks.

  This patch only rejects REG_SP in "reject_bad_reg" and several related places
for legacy architectures before ARMv8-A. I have checked those affected instructions
, all of them qualify such relaxations.

  Testcases adjusted accordingly.
    * ld-sp-warn.d was written without .arch and without -march options passed.
      By default it assumes all architectures, so I deleted the REG_SP warning
      on ldrsb as it's supported on ARMv8-A.  There are actually quite a few
      seperate tests on other architectures, for example ld-sp-warn-v7.l etc.,
      so there the test for ldrsb on legacy architectures are still covered.
    * sp-pc-validations-bad-t has been extended to armv8-a.
    * strex-bad-t.d restricted on armv7-a.
    * Some new tests for REG_SP used as Rd/Rt etc added in sp-usage-thumb2-relax*.

gas/
	* config/tc-arm.c (reject_bad_reg): Allow REG_SP on ARMv8-A.
	(parse_operands): Allow REG_SP for OP_oRRnpcsp and OP_RRnpcsp on
	ARMv8-A.
	(do_co_reg): Allow REG_SP for Rd on ARMv8-A.
	(do_t_add_sub): Likewise.
	(do_t_mov_cmp): Likewise.
	(do_t_tb): Likewise.
	* testsuite/gas/arm/ld-sp-warn.l: Delete the warning on REG_SP as Rt for
	ldrsb.
	* testsuite/gas/arm/sp-pc-validations-bad-t-v8a.d: New test.
	* testsuite/gas/arm/sp-pc-validations-bad-t-v8a.l: New test.
	* testsuite/gas/arm/sp-pc-validations-bad-t.d: Specifies -march=armv7-a.
	* testsuite/gas/arm/sp-pc-validations-bad-t.s: Remove ".arch armv7-a".
	* testsuite/gas/arm/sp-usage-thumb2-relax-on-v7.d: New test.
	* testsuite/gas/arm/sp-usage-thumb2-relax-on-v7.l: New test.
	* testsuite/gas/arm/sp-usage-thumb2-relax-on-v8.d: New test.
	* testsuite/gas/arm/sp-usage-thumb2-relax.s: New test.
	* testsuite/gas/arm/strex-bad-t.d: Specifies -march=armv7-a.