Add support for line drawing characters and the alternate character set.

Add support for line drawing characters and the alternate character set.
This enables using the ACS_ curses macros with libpayload.

The translation from ACS_ macros (or characters with attribute A_ALTCHARSET)
is done using one acs map for the video console, one for serial console
(xterm/vt100/vt220), and one fallback, from which an ASCII substitute is
taken if the device specific map doesn't contain an entry (ie NUL).

Signed-off-by: Ulf Jordan <jordan@chalmers.se>
Acked-by: Jordan Crouse <jordan.crouse@amd.com>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@3499 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1