bhyve: Fix synopsis in the usage message

In particular:
- Sort short options to align with style(9)
- Add two missing flags: -G and -r
- Drop unnecessary angle brackets for consistency
- Rename the "vm" argument to vmname for consistency with the manual
  page

MFC after:	2 weeks

usr.sbin/bhyve/bhyverun.c

@@ -222,10 +222,10 @@ usage(int code)
 {
 
         fprintf(stderr,
-		"Usage: %s [-aehuwxACDHPSWY]\n"
+		"Usage: %s [-AaCDeHhPSuWwxY]\n"
 		"       %*s [-c [[cpus=]numcpus][,sockets=n][,cores=n][,threads=n]]\n"
-		"       %*s [-k <file>] [-l <lpc>] [-m mem] [-o <var>=<value>]\n"
-		"       %*s [-p vcpu:hostcpu] [-s <pci>] [-U uuid] [<vm>]\n"
+		"       %*s [-G port] [-k file] [-l lpc] [-m mem] [-o var=value]\n"
+		"       %*s [-p vcpu:hostcpu] [-r file] [-s pci] [-U uuid] vmname\n"
 		"       -a: local apic is in xAPIC mode (deprecated)\n"
 		"       -A: create ACPI tables\n"
 		"       -c: number of cpus and/or topology specification\n"