(mips_addr_bits_remove): Test mask_address_p to decide whether
to mask off the upper 32 bits of addresses.
(_initialize_mips_tdep): Add command to set mask_address_p.
(mips_call_dummy_address): New function.
* config/mips/tm-mips.h (CALL_DUMMY_ADDRESS): Redefine to
call mips_call_dummy_address.