menu: fix timeout duration

menu: fix timeout duration

For distro-boot, the TIMEOUT directive in the boot script specifies
how long to pause in units of 1/10 sec. [1]

Commit 8594753ba0a7 ("menu: only timeout when menu is displayed")
corrected this by simply dividing the timeout value by 10 in
menu_interactive_choice().

I see two problems:

 - For example, "TIMEOUT 5" should wait for 0.5 sec, but the current
   implementation cannot handle the granularity of 1/10 sec.
   In fact, it never breaks because "m->timeout / 10" is zero,
   which means no timeout.

 - The menu API is used not only by cmd/pxe.c but also by
   common/autoboot.c .  For the latter case, the unit of the
   timeout value is _second_ because its default is associated
   with CONFIG_BOOTDELAY.

To fix the first issue, use DIV_ROUND_UP() so that the timeout value
is rounded up to the closest integer.

For the second issue, move the division to the boundary between
cmd/pxe.c and common/menu.c .  This is a more desirable place because
the comment of struct pxe_menu says:

 * timeout - time in tenths of a second to wait for a user key-press before
 *           booting the default label.

Then, the comment of menu_create() says:

 * timeout - A delay in seconds to wait for user input. If 0, timeout is
 * disabled, and the default choice will be returned unless prompt is 1.

[1] https://www.syslinux.org/wiki/index.php?title=SYSLINUX#TIMEOUT_timeout

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>