bd_info: remove bi_barudrate member from struct bd_info

gd->bd->bi_baudrate is a copy of gd->baudrate.

Since baudrate is a common feature for all architectures,
keep gd->baudrate only.

It is true that bi_baudrate was passed to the kernel in that structure
but it was a long time ago.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Tom Rini <trini@ti.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Heiko Schocher <hs@denx.de>
Acked-by: Michal Simek <monstr@monstr.eu> (For microblaze)