Rocket updates for zfh-extension

[kiratsao]

This PR is going to implement an option for the Half-Precision Unit in FPU.scala
With minFLen = 16, will enable the control signals decode table.

The typeTagIn/typeTagOut numbers will automatically generate according to below settings:

S:       S=0
S, D:    S=0, D=1
H. S:    H=0, S=1
H, S, D: H=0, S=1, D=2

The major changes are inside FPU.scala:

• define H/S/D/I
• Update control signals table
• Change singleIn/singleOut to typeTagIn/typeTagOut

Type of change: feature request

Impact: API addition (no impact on existing code)

Development Phase: implementation