arm: Fix an incorrect warning when -mcpu=cortex-a55 is used with -mfloat-abi=soft

arm: Fix an incorrect warning when -mcpu=cortex-a55 is used with -mfloat-abi=soft

When a CPU such as cortex-a55 is used with the soft-float ABI variant,
the compiler is incorrectly issuing a warning about a mismatch between
the architecture (generated internally) and the CPU.  This is not
expected or intended.

The problem stems from the fact that we generate (correctly) an
architecture for a soft-float compilation, but then try to compare it
against the one recorded for the CPU.  Normally we strip out the
floating point information before doing that comparison, but we
currently only do that for the features that can be affected by the
-mfpu option.  For a soft-float environment we also need to strip out
any bits that depend on having floating-point present.

So this patch implements that and does a bit of housekeeping at the
same time:

- in arm-cpus.in it is not necessary for a CPU to specify both
  +dotprod and +simd in its architecture specification, since +dotprod
  implies +simd.

- I've refactored the ALL_SIMD fgroup in arm-cpus.in to create a new
  subgroup ALL_SIMD_EXTERNAL and containing the bits that were
  previously added directly to ALL_SIMD.  Similarly, I've added an
  ALL_FPU_EXTERNAL subgroup.

- in arm.c rename fpu_bitlist and all_fpubits to fpu_bitlist_internal
  and all_fpubits_internal for consistency with the fgroup bits which
  they contain.

	* config/arm/arm-cpus.in (ALL_SIMD_EXTERNAL): New fgroup.
	(ALL_SIMD): Use it.
	(ALL_FPU_EXTERNAL): New fgroup.
	(ALL_FP): Use it.
	(cortex-a55, cortex-a75, cortex-a76, cortex-a76ae): Remove redundant
	+simd from architecture specification.
	(cortex-a77, neoverse-n1, cortex-a75.cortex-a55): Likewise.
	* config/arm/arm.c (isa_all_fpubits, fpu_bitlist): Rename to ...
	(isa_all_fpubits_internal, fpu_bitlist_internal): ... these.
	(isa_all_fpbits): New bitmap.
	(arm_option_override): Initialize it.
	(arm_configure_build_target): If the target isa does not have any
	FP enabled, do not warn about mismatches in FP-related feature bits.

From-SVN: r279219