core/driver: Switch hypervisor to fixed virtual address layout

core/driver: Switch hypervisor to fixed virtual address layout

Now that the driver always puts us at the same virtual address, we can
compile this into the hypervisor as well. On x86, we switch to the code
model "kernel", i.e. all virtual addresses have the higher 32 bits set.
This allows to drop -fpic and -fpie, the global offset table. And the
entry field in the header is now absolute.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>