Use Linux custom baud rate selection based on struct termios2.

Use Linux custom baud rate selection based on struct termios2.

This new mechanism is preferred as it is supported by newer Linux serial
UART drivers such as TI OMAP.

BUG=422165
TEST=Wired together FTDI and CP2102 USB serial adapters and tried standard and non-standard bitrates.

Committed: https://crrev.com/3ecad604443848aed3091641652f1c943cb212a7
Cr-Commit-Position: refs/heads/master@{#329016}

[Reilly Grant (use Gerrit), 2015-05-07 20:30:18]

reillyg@chromium.org changed reviewers:
+ rockot@chromium.org

[Reilly Grant (use Gerrit), 2015-05-07 20:30:19]

Please take a look.

[Ken Rockot(use gerrit already), 2015-05-08 19:29:51]

lgtm

[Reilly Grant (use Gerrit), 2015-05-08 19:32:50]

The CQ bit was checked by reillyg@chromium.org

[commit-bot: I haz the power, 2015-05-08 19:34:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1131953003/1

[commit-bot: I haz the power, 2015-05-08 19:39:20]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-08 19:40:09]

Patchset 1 (id:??) landed as
https://crrev.com/3ecad604443848aed3091641652f1c943cb212a7
Cr-Commit-Position: refs/heads/master@{#329016}