cfg: refactor lpc1xxx targets onto one base config

Since now auto-detection for flash size works nicely, there's no
reason to keep numerous configs around.

Change-Id: If0cbc37985abf17ef7c1f7d0688e76500fac228f
Signed-off-by: Vanya Sergeev <vsergeev@gmail.com>
Reviewed-on: http://openocd.zylin.com/1960
Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>