executor/kvm: bug fix and minor refactor in KVM

* Fixes a bug when setting up a 64-bit guest by making the bit
  manipulation macros produce unsigned long long: To create a VCPU that
  has paging enabled, one needs to set the CR0.PE and CR0.PG bits in
  CR0. The latter is problematic when setting up a 64-bit guest since if
  the macro is not using 1ULL, it sign extends the output (in 64-bit
  mode the control registers are extended to 64-bits with some of the
  CR0[32:63] bits reserved). This results in either failing the
  KVM_SET_SREGS ioctl (in newer kernel versions) or just failing the
  KVM_RUN ioctl with EXIT_REASON_INVALID_STATE.

* Moved the bit manipulation definitions from the amd64 specific to the generic
  kvm header to consolidate them with the already existing ones.
  Prefixed them with X86_ to avoid confusion.

Author: marpom