kboot: Implement dup(2)

Early in boot, we need to create the normal stdin/out/err env for the
boot loader to run in. To do that, we need to open the console and
duplicate the file descriptors which requires dup(2). Implement a
wrapper as host_dup.

Sponsored by:		Netflix

stand/kboot/arch/amd64/syscall_nr.h

@@ -1,4 +1,5 @@
 #define SYS_close		  3
+#define	SYS_dup			 32
 #define SYS_getdents		 78
 #define	SYS_getpid		 39
 #define SYS_gettimeofday	 96

stand/kboot/arch/powerpc64/syscall_nr.h

@@ -1,4 +1,5 @@
 #define SYS_close		  6
+#define	SYS_dup			 41
 #define SYS_fstat		108
 #define SYS_getdents		141
 #define	SYS_getpid		 20

stand/kboot/host_syscall.h

@@ -92,6 +92,7 @@ struct host_timeval {
  * System Calls
  */
 int host_close(int fd);
+int host_dup(int fd);
 int host_fstat(int fd, struct host_kstat *sb);
 int host_getdents(int fd, void *dirp, int count);
 int host_getpid(void);

stand/kboot/host_syscalls.c

@@ -13,6 +13,12 @@ host_close(int fd)
 	return host_syscall(SYS_close, fd);
 }
 
+int
+host_dup(int fd)
+{
+	return host_syscall(SYS_dup, fd);
+}
+
 int
 host_fstat(int fd, struct host_kstat *sb)
 {