Add empty opcode header files for half-precision

* Update riscv/opcodes.h through the riscv-opcodes repository.
Add missing fcvt opcodes through riscv-opcodes
Merge branch 'master' of github.com:ucb-bar/riscv-isa-sim into confprec
Implement "half-baked" half-precision instruction subset for Hwacha
Re-add Hwacha header file
Fix declaration of half-precision instructions
Merge branch 'master' of github.com:ucb-bar/riscv-isa-sim into HEAD
Add vsetprec instruction prototype
Remove debug printf in vsetprec
Merge branch 'confprec'

Conflicts:
	hwacha/hwacha.mk.in