Float operands not always start with 'f' Zfinx for example

[ptprasanna]

riscv-isac/riscv_isac/InstructionObject.py

Line 303 in 9dc9503

if 'rs1' in instr_vars and instr_vars['rs1'] is not None and instr_vars['rs1'].startswith('f'):

The condition of invoking the define_sem function should not be of the registers starting with f. The solution has to be generalized rather hard-coding the register's alphabets.

P.S: Ideally these changes/revisions in the framework should've taken place after Z_inx PR is merged.