uboot-imx

dm: serial: consolidate common code more

Commit b8893327e9d2 (dm: serial: Put common code into separate functions)
consolidated getc() and putc().  This commit does more puts() and tsts().

Also rename locally used functions to _serial_*() for clarification
because we have similar functions names here are there in this file.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>