x86: Privatize names of static vendor-specific functions

x86: Privatize names of static vendor-specific functions

vcpu_set_cell_config, vcpu_reset, vcpu_vendor_get_io_intercept and
vcpu_vendor_get_pf_intercept - they share the same parameters across the
vendor-specific implementations, but they are invoked only locally. So
rename them to something which is prefixed by vmx and svm, respectively,
so that they can be locally refactored as desired with risking confusion
that they might have to usable in a cross-vendor fashion.

CC: Valentine Sinitsyn <valentine.sinitsyn@gmail.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>