[Patch][binutils][arm] .bfloat16 directive for Arm [6/X]

[Patch][binutils][arm] .bfloat16 directive for Arm [6/X]

Hi,

This patch is part of a series that adds support for Armv8.6-A
(Matrix Multiply and BFloat16 extensions) to binutils.

This patch implements the '.bfloat16' directive for the Arm backend.

The syntax for the directive is:
  .bfloat16 <0-n numbers>
e.g.
  .bfloat16 12.0
  .bfloat16 0.123, 1.0, NaN, 5

This is implemented by utilizing the ieee_atof_detail function (included
in the previous patch) in order to encode the slightly different
bfloat16 format.

Added testcases to verify the correct encoding for various bfloat16
values (NaN, Infinity (+ & -), normals, subnormals etc...).

Cross compiled and tested on arm-none-eabi and arm-none-linux-gnueabihf
with no issues.

Committed on behalf of Mihail Ionescu.

gas/ChangeLog:

2019-10-21  Mihail Ionescu  <mihail.ionescu@arm.com>
2019-10-21  Barnaby Wilks  <barnaby.wilks@arm.com>

	* config/tc-arm.c (md_atof): Add encoding for bfloat16
	* testsuite/gas/arm/bfloat16-directive-le.d: New test.
	* testsuite/gas/arm/bfloat16-directive-be.d: New test.
	* testsuite/gas/arm/bfloat16-directive.s: New test.

Is it ok for trunk?

Regards,
Mihail