tty: serial: bcm63xx: Eliminate unnecessary request/release functions

We don't really need to perform the ioremap "on demand" so it's simpler
just to do it from the probe function.  This also lets us eliminate the
UART_REG_SIZE constant and rely on the resource information passed in
from the DT or platform code.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>