[coreboot] Warnings

[Myles Watson]

As of 5512, these are the last four warnings that are not "defined but
not used" warnings.

src/northbridge/amd/gx2/chipsetinit.c:271: warning: suggest
parentheses around '-' inside '<<'
src/northbridge/amd/lx/raminit.c:334: warning: array subscript is
above array bounds
src/northbridge/via/vx800/pci_rawops.h:43:2: warning: #warning "FIXME:
get rid of this extra copy of pci access functions."
src/southbridge/intel/pxhd/pxhd_bridge.c:70:2: warning: #warning
"Please review lots of dead code here."

Thanks,
Myles