x86: Fix MSRPM in x2APIC mode

Only x2APIC-related MSRs are whitelisted now if x2APIC is enabled.
x86: Rudimentary guest MTRR emulation support

Implemented rough MTRR Enable bit (MTRR defType) emulation. This is
required for Linux CPU bootstrapping code to work properly, and fixes
a CPU lockup bug that occurs when destroying a cell on some AMD boards.
configs: Added Gigabyte GA-F2A88XM-HD3 board

Added the config file for another AMD-based board which can be used
to test AMD-V port.