* remote.c: Make it work for embedded MIPS. Increase buffer

* remote.c:  Make it work for embedded MIPS.  Increase buffer
size, and use throughout.  Round buffer size up if too many regs.
Support baud rate setting and try for an 8-bit path.  If
interrupted while waiting for target, send a ^C down the wire.
Avoid single-byte reads.
* tm-mips.h:  Add more embedded-system registers to REGISTER_NAMES
and NUM_REGS.
* mips-xdep.h:  Avoid the embedded regs when on Unix.