8250/16?50: Add support for Broadcom TruManage redirected serial port

commit ebebd49a8eab5e9aa1b1f8f1614ccc3c2120f886 upstream.

Add support for the UART device present in Broadcom TruManage capable
NetXtreme chips (ie: 5761m 5762, and 5725).

This implementation has a hidden transmit FIFO, so running in single-byte
interrupt mode results in too many interrupts.  The UART_CAP_HFIFO
capability was added to track this.  It continues to reload the THR as long
as the THRE and TSRE bits are set in the LSR up to a specified limit (1024
is used here).

Signed-off-by: Stephen Hurd <shurd@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2:
 - Adjust filenames
 - Adjust context
 - First available port type number is 22 not 24
 - s/uart_8250_port/uart_port/
 - Use serial_in() not serial_port_in()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>