input: Add ANSI 3.64 escape sequence generation.

To support Non-ASCII keys (ex, Fn, PgUp/Dn, arrow keys, ...), we need to
translate key code into escape sequence.

(Updated by sjg@chromium.org to move away from a function to store
keycodes, so we can easily record how many were sent. We now need to
return this from input_send_keycodes() so we know whether keys were
generated.)

Signed-off-by: Hung-Te Lin <hungte@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Rini <trini@ti.com>