serial: pl01x: fix PL010 regression

commit aed2fbef
"dm: serial: Tidy up the pl01x driver"
caused a regression on (real hardware) PL010 by omitting
to update the line control register when switching baudrate.

Fix this by inlining the missing write to the baud control
register.

Also renaming the set_line_control() function to
pl011_set_line_control() since this function is clearly
PL011-specific, and it won't suffice to call that to
set up line control.

Tested on the Integrator/AP hardware.

Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>