* regcache.h: Update copyright.

* regcache.h: Update copyright.
(struct regcache, struct gdbarch): Add opaque declarations.
(current_regcache): Declare global variable.
(regcache_read, regcache_write): Add gdbarch parameter.
(regcache_save, regcache_save_no_passthrough)
(regcache_restore, regcache_restore_no_passthrough)
(regcache_dup, regcache_dup_no_passthrough)
(regcache_cpy, regcache_cpy_no_passthrough)
(deprecated_grub_regcache_for_registers)
(deprecated_grub_regcache_for_register_valid)
(regcache_valid_p): Add function declarations.

* regcache.c: Update copyright.
(regcache_descr_handle): New global variable.
(struct regcache_descr): Define.
(init_legacy_regcache_descr, init_regcache_descr): New functions.
(regcache_descr, xfree_regcache_descr): New functions.
(struct regcache): Define.
(regcache_xmalloc, regcache_xfree): New functions.
(regcache_cpy, regcache_cpy_no_passthrough): New functions.
(regcache_dup, regcache_dup_no_passthrough): New functions.
(regcache_valid_p, regcache_read_as_address): New functions.
(deprecated_grub_regcache_for_registers): New function.
(deprecated_grub_regcache_for_register_valid): New function.
(current_regcache): New global variable.
(register_buffer): Add regcache parameter.  Update calls.
(regcache_read, regcache_write): Add regcache parameter.  Rewrite.
(read_register_gen, write_register_gen): Update register_buffer
call.  Test for legacy_p instead of gdbarch_register_read_p or
gdbarch_register_write_p.
(regcache_collect): Update register_buffer call.
(build_regcache): Rewrite.  Use deprecated grub functions.
(regcache_save, regcache_save_no_passthrough): New functions.
(regcache_restore, regcache_restore_no_passthrough): New
functions.
(_initialize_regcache): Create the regcache_data_handle. Swap
current_regcache global variable.

* sh-tdep.c (sh_pseudo_register_read): Add current_regcache
parameter to regcache_read and regcache_write calls.
(sh4_register_read): Ditto.
(sh64_pseudo_register_read): Ditto.
(sh64_register_read): Ditto.
(sh_pseudo_register_write): Ditto.
(sh4_register_write): Ditto.
(sh64_pseudo_register_write): Ditto.
(sh64_register_write): Ditto.

* defs.h (XCALLOC): Define.