ArmPkg/ArmSoftFloatLib: switch to new version of softfloat library

ArmPkg/ArmSoftFloatLib: switch to new version of softfloat library

Update the INF description and the top level .c files in order to
switch to the new version of the SoftFloat library imported as a
Git submodule in the previous patch.

Note that we no longer use the code that travelled a long way from
the 2002 version of the softfloat library via NetBsd and the StdLib
package. Instead, we are using the upstream version unmodified, with
the glue .c file adopted from the OP-TEE project. This approach is
much cleaner and much more maintainable.

Note that support for the RVCT toolchains is being dropped at the same
time. RVCT is mostly untested, and planned to be removed, and so it
makes little sense to go to the trouble of upgrading this library for
RVCT as well.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1845
Acked-by: Jian J Wang <jian.j.wang@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>