gdb: fix size of z80 "add ii,rr" and "ld (ii+d),n" instructions

gdb: fix size of z80 "add ii,rr" and "ld (ii+d),n" instructions

The tables in z80-tdep.c previously either gave these instructions the
wrong size, or failed to recognize them by using the wrong masks, or
both. The fixed instructions alongside their representation in octal are:

* add ii,rr:   [0335] 00r1 (where r & 1 == 1)
               [0375] 00r1
* ld (ii+d,n): [0335] 0066 <d> <n>
               [0375] 0066 <d> <n>

Prefix bytes inside [] do not count towards instruction length in
these tables.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33066
Approved-By: Tom Tromey <tom@tromey.com>