Include PowerPC SPR numbers for special-purpose registers.

Include PowerPC SPR numbers for special-purpose registers.
* rs6000-tdep.c (struct reg): Add new member, 'spr_num'.
(R, R4, R8, R16, F, P, R32, R64, R0): Include value for
new member in initializer.
(S, S4, SN4, S64): New macros for defining special-purpose
registers.
(PPC_UISA_SPRS, PPC_UISA_NOFP_SPRS, PPC_OEA_SPRS, registers_power,
registers_403, registers_403GC, registers_505, registers_860,
registers_601, registers_602, registers_603, registers_604,
registers_750, registers_e500): Use them.