tty: serial: amba-pl010: use more uart_port pointers

tty: serial: amba-pl010: use more uart_port pointers

The code uses uart_amba_port::port on many places. Sometimes it even
needs not uart_amba_port itself. So simplify the code on many places
and remove the need of uart_amba_port on some places completely.

No functional changes intended. The objdump -d output shows only a code
move in pl010_rx_chars().

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Russell King <linux@armlinux.org.uk>
Link: https://lore.kernel.org/r/20220224111028.20917-5-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>