Inclusion of shifter from https://github.com/riscv/riscv-bitmanip/blob/main-history/verilog/rvb_shifter/rvb_shifter.v

Created by: Silabs-ArjanB

DO NOT MERGE YET

Line 160 - 277 of cv32e40x_alu.sv in this pull request are based on a (slightly modified) copy of https://github.com/riscv/riscv-bitmanip/blob/main-history/verilog/rvb_shifter/rvb_shifter.v

The file now contains two copyright notices (line 1and line 162).

The 'bit manipulation github repos from which the code was copied also contains the following license info: https://github.com/riscv/riscv-bitmanip/blob/main-history/LICENSE

Signed-off-by: Arjan Bink Arjan.Bink@silabs.com