[ARM] 4982/1: [AT91] Drop old-style UART initialization (Part 1)

All the SAM9 boards supported by mainline and the AT91 patches have
been converted to the new-style UART initialization.  Therefore drop
support for the old at91_init_serial() interface for SAM9.

at91_uarts[] array can also be marked as __initdata.

The warning that no serial-console is defined moved from
at91_set_serial_console() to at91_add_device_serial() since the whole
point is the board-specific file is not calling
at91_set_serial_console().

Signed-off-by: Andrew Victor <linux@maxim.org.za>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>