lpc4350_spifi_generic: Clean up work area size

lpc4350_spifi_generic: Clean up work area size

Since 2cbbe9a it was actually decreasing the configured work area size.

We could now do "set WORKAREASIZE 0x2000" before sourcing lpc4350.cfg,
but there seems no point in doing so. Simply drop the configuration here.

Change-Id: I25b9dbbc007ba652b66099832198b7c329929858
Signed-off-by: Andreas Färber <afaerber@suse.de>
Reviewed-on: http://openocd.zylin.com/3086
Tested-by: jenkins
Reviewed-by: Karl Palsson <karlp@tweak.net.au>
Reviewed-by: Paul Fertser <fercerpav@gmail.com>