northbridge/intel/i440bx: Registered SDRAM modules support and fixes

northbridge/intel/i440bx: Registered SDRAM modules support and fixes

Adds support for initializing registered SDRAM modules on
Intel 440BX northbridge.

Drops unneeded romcc-inspired programming tricks.

Only set nbxecc flags (see 440BX datasheet, page 3-16) when
a non-ECC module has been detected in a row via SPD; also
drops an unneeded intermediate variable used in setting them.

Boot tested on ASUS P2B-LS with regular and registered ECC
SDRAM under Linux and memtest86+.

Change-Id: Idc99d49567cca55f819d6b0e98952b1c3256498a
Signed-off-by: Keith Hui <buurin@gmail.com>
Reviewed-on: http://review.coreboot.org/128
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>