xen: remove xen_domain_type enum/variable

The vm_guest variable readily covers all uses of xen_domain_type, so
merge them together. Since support for PV domains has been removed
hard-core xen_pv_domain() to return false.

Reviewed by: royger

sys: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

sys: Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

xen: move vcpu_info to common, leave hook for setup

vcpu_info is crucial for the Xen event channel core. Since both the
data and setup steps are identical between architectures, move them to
the common file. Since there is no cross-architecture method to call
a function on every processor during bring-up, simply leave the setup
function.

The number of vcpu_info structures available on the shared information
page varies by architecture. Instead of hard-coding the count use
nitems(). Add a warning message for this being used.

Switch to XEN_VCPUID() and use Xen's typedefs.

panic() on failure since >32 processors is no longer unusual.

royger: Specify 64-byte alignment for vcpu_info to try to defend
against vcpu_info crossing a page boundary. Add detection for this
limit.

Reviewed by: royger

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

xen: move common variables off of sys/x86/xen/hvm.c

The xen_domain_type and HYPERVISOR_shared_info variables are shared by
all Xen architectures, so they should be in common rather than
reimplemented by each architecture.

hvm_start_flags is used by xen_initial_domain() and so needs to be in
common.

Reviewed by: royger
Differential Revision: https://reviews.freebsd.org/D28982