fix disabling of the calypso bootrom on targets with nIBOOT tied to low:

fix disabling of the calypso bootrom on targets with nIBOOT tied to low:
* bit 8 always needs to be 1 when overriding the setting of the nIBOOT pin, so now we set both bits (9 and 8) to 1, and clear bit 9 if we want to enable the romloader
* to be sure, this was tested on a target with nIBOOT high (C155) and a Alcatel VLE5 pulled to low, and works fine

Signed-off-by: Steve Markgraf <steve@steve-m.de>