Select the Solaris/illumos os-support backend for Hammerhead in the Xorg DDX.

hw/xfree86/os-support/meson.build picks the per-OS console backend from
host_machine.system(). On Hammerhead uname sysname is "hammerhead", not
"sunos", so the `elif host_machine.system() == 'sunos'` arm never fires and
the build silently falls through to the generic *stub* backend (stub_init.c,
VTsw_noop, etc.). That stub is a no-op: xf86OpenConsole() does nothing, so the
server never touches /dev/console / VT_SETDISPINFO and can't drive the
framebuffer console the M2 illumosfb driver targets.

Hammerhead IS illumos, so the solaris arm (sun_init.c: /dev/console +
VT_SETDISPINFO, sun_vid.c, sun_apm/bell, solaris-amd64.S port I/O) is exactly
the load-bearing console layer we need. Extend the guard to match Hammerhead's
sysname, mirroring the os/meson.build sunos-sysname patch (0001).

--- a/hw/xfree86/os-support/meson.build
+++ b/hw/xfree86/os-support/meson.build
@@ -62,7 +62,7 @@ if host_machine.system() == 'linux'
         srcs_xorg_os_support += 'shared/pm_noop.c'
     endif

-elif host_machine.system() == 'sunos'
+elif host_machine.system() == 'sunos' or host_machine.system() == 'hammerhead'
     srcs_xorg_os_support += [
         'solaris/sun_apm.c',
         'solaris/sun_bell.c',