ArmPkg: ARM v8.2 updates for detecting FP

The ARMv8.2-FP16 extension introduces support for half precision
floating point and the processor ID registers have been updated to
enable detection of the implementation.

The possible values for the FP bits in ID_AA64PFR0_EL1[19:16] are:
  - 0000 : Floating-point is implemented.
  - 0001 : Floating-point including Half-precision support is
           implemented.
  - 1111 : Floating-point is not implemented.
  - All other values are reserved.

Previously ArmEnableVFP() compared the FP bits with 0000b to see if
the FP was implemented, before enabling FP. Modified this check to
enable the FP if the FP bits 19:16 are not 1111b.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Signed-off-by: Evan Lloyd <evan.lloyd@arm.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>