Mention "lpc4300" (with "lpc1800" alias) flash drivers in manual

Change-Id: I0bb28910b2c07b1ca5bd644e0d88b931d585d3e7
Signed-off-by: Freddie Chopin <freddie.chopin@gmail.com>
Reviewed-on: http://openocd.zylin.com/1352
Tested-by: jenkins