timer: atmel_tcb_timer: add atmel_tcb driver

Add a driver for the timer counter block that can be found on sama5d2.
This driver will be used when booting under OP-TEE since the pit timer
which is part of the SYSC is secured. Channel 1 & 2 are configured to
be chained together which allows to have a 64bits counter.

Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Clément Léger <clement.leger@bootlin.com>