* alpha-tdep.h: New file. Includes several Alpha target constants

* alpha-tdep.h: New file.  Includes several Alpha target constants
taken from...
* config/alpha/tm-alpha.h: ...here.  Remove macros that we now
let gdbarch deal with.
(GDB_MULTI_ARCH): Define as GDB_MULTI_ARCH_PARTIAL.
* Makefile.in (alpha-nat.o): Add alpha-tdep.h and $(BFD_SRC)/elf-bfd
to dependency list.
* alpha-nat.c: Include alpha-tdep.h.  Update for adjusted
Alpha target register names.
* alphabsd-nat.c: Likewise.
* alpha-tdep.c: Include alpha-tdep.h.  Update for adjusted
Alpha target register names.  Make serveral routines static.
(alpha_get_saved_register): New function.
(alpha_abi_names): New.
(process_note_abi_tag_sections): New function.
(get_elfosabi): New function.
(alpha_gdbarch_init): New function.
(alpha_dump_tdep): New function.
(_initialize_alpha_tdep): Register alpha_gdbarch_init.