linux: Prepare to run with multiple hypervisors
linux: Prepare to run with multiple hypervisors

Move KVM-specific code to "run_kvm" function in preparation for
supporting different hypervisors.

Change-Id: I02b81478ded893a0ee67e132f12d637912491fea
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3586011
Reviewed-by: Dmitry Torokhov <10a8c465cefc9bdd6c925e26964d23c90f1141cc@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: Steven Moreland <4840f2e2fca2d2af23b5ddcdd6ec59bfb2c968b2@google.com>

google/crosvm,google/crosvm,google/crosvm,google/crosvm