[U-Boot] mpc83xx: update LCRR register handling

MPC8379E RM says (10-34): Once LCRR[CLKDIV] is written, the register should be read, and then an isync should be executed. So update this in code. Also define a LCRR mask for processors, which uses not all bits in the LCRR register (as for example mpc832x did). Signed-off-by: Heiko Schocher

Re: [U-Boot] mpc83xx: update LCRR register handling

MPC8379E RM says (10-34): Once LCRR[CLKDIV] is written, the register should be read, and then an isync should be executed. So update this in code. Also define a LCRR mask for processors, which uses not all bits in the LCRR register (as for example mpc832x did). Signed-off-by: Heiko