x86: Map guest memory in svm_cpu_park()

Map guest memory before copying CPU parking code into it. This fixes
a #PF that occurs when CPU is parked. Also align parking code GPA on
page boundary.
x86: Fix real mode cells in x86_parse_mov_to_cr()

Added support for non-paged cells in x86_parse_mov_to_cr(), reworked
its code and fixed some small bugs. This allows to use the function
for apic-demo.cell and other inmates on hosts where decode assists are
not available.
x86: Fix code formatting