* sparc-tdep.h (struct regset): Provide opaque declaration.

* sparc-tdep.h (struct regset): Provide opaque declaration.
(struct gdbarch_tdep): Add gregset, sizeof_gregset,
fpregset and sizeof_fpregset members.
* sparc-tdep.c (struct regset): Provide opaque declaration.
(sparc_regset_from_core_section): New function.
(sparc32_gdbarch_init): Initialize TDEP->gregset,
TDEP->sizeof_gregset, TDEP->fpregset and TDEP->sizeof_fpregset.
Set regset_from_core_section when appropriate.