z80: Make generic op functions for first couple load ops.

I had an idea to pass pointers to registers into the operation
functions to make a single "inc 16 bit register" style function, for
example. Wrapper functions will call these functions and pass the
appropriate registers in for the different opcodes.
z80: Make generic load 8bit immidiate into register function.
z80: Make generic function to increment a 16 bit register.
z80: Make generic function to increment an 8 bit register.
z80: Make generic function to RLC an 8 bit register.