x86: set accessed bit in ROM-based GDT

Previous configuration was backwards. From the Intel manual:

"If the segment descriptors in the GDT or an LDT are placed in ROM,
the processor can enter an indefinite loop if software or the
processor attempts to update (write to) the ROM-based segment
descriptors. To prevent this problem, set the accessed bits
for all segment descriptors placed in a ROM. Also, remove
operating-system or executive code that attempts to modify
segment descriptors located in ROM."

Only by some miracle has this not been causing problems.

Change-Id: I0bb915962a1069876d2486473760112102feae7b
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>