Added SPIFI flash driver, algorithms, and docs

Added SPIFI flash driver, algorithms, and docs

Added a flash driver designed to allow program/erase of
memory-mapped SPI flash chips for LPC43xx/LPC18xx family
micros. This driver includes three algorithms - erase,
write, and SPIFI peripheral initialization (to allow
memory-mapped access after a reset). The driver has been
added to the flash driver table (drivers.c), and the
OpenOCD documentation has been updated to include the flash
driver configuration command.

Change-Id: I79f4ff8f1f07de4e5f2fe4f8c23aeb903f868514
Signed-off-by: George Harris <george@luminairecoffee.com>
Reviewed-on: http://openocd.zylin.com/783
Tested-by: jenkins
Reviewed-by: Aurelien Jacobs <aurel@gnuage.org>
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>