cpu/lpc2387: clear BODR if POR is set
cpu/lpc2387: clear BODR if POR is set

From the data sheet:

> **Note:** Only in case when a reset occurs and the POR = 0, the BODR bit
indicates if the V DD(DCDC)(3V3) voltage was below 2.6 V or not.

So the value of BODR is undefined if POR is set.
Clear it to bring it to a defined state.

authmillenon/RIOT,jasonatran/RIOT,ant9000/RIOT,OTAkeys/RIOT,ant9000/RIOT,miri64/RIOT,yogo1212/RIOT,yogo1212/RIOT,basilfx/RIOT,OTAkeys/RIOT,smlng/RIOT,ant9000/RIOT,OlegHahm/RIOT,smlng/RIOT,kYc0o/RIOT,jasonatran/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,miri64/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,miri64/RIOT,kaspar030/RIOT,jasonatran/RIOT,authmillenon/RIOT,kYc0o/RIOT,smlng/RIOT,smlng/RIOT,jasonatran/RIOT,authmillenon/RIOT,authmillenon/RIOT,kaspar030/RIOT,ant9000/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,kaspar030/RIOT,OlegHahm/RIOT,miri64/RIOT,smlng/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,ant9000/RIOT,kaspar030/RIOT,yogo1212/RIOT,OTAkeys/RIOT,authmillenon/RIOT,OlegHahm/RIOT,basilfx/RIOT,OTAkeys/RIOT,jasonatran/RIOT,kYc0o/RIOT,authmillenon/RIOT,basilfx/RIOT,OlegHahm/RIOT,yogo1212/RIOT,yogo1212/RIOT,basilfx/RIOT,yogo1212/RIOT,miri64/RIOT,basilfx/RIOT,kaspar030/RIOT