Add CLI and multilib support for Armv8.1-M Mainline MVE extensions

Add CLI and multilib support for Armv8.1-M Mainline MVE extensions

gcc/ChangeLog:

2020-01-16  Mihail Ionescu  <mihail.ionescu@arm.com>
2020-01-16  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	* config/arm/arm-cpus.in (mve, mve_float): New features.
	(dsp, mve, mve.fp): New options.
	* config/arm/arm.h (TARGET_HAVE_MVE, TARGET_HAVE_MVE_FLOAT): Define.
	* config/arm/t-rmprofile: Map v8.1-M multilibs to v8-M.
	* doc/invoke.texi: Document the armv8.1-m mve and dps options.

gcc/testsuite/ChangeLog:

2020-01-16  Mihail Ionescu  <mihail.ionescu@arm.com>
2020-01-16  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	* testsuite/gcc.target/arm/multilib.exp: Add v8.1-M entries.