clk: at91: add PMC macro file for dt definitions

This patch adds a new macro file for PMC macros.

This macro file includes the definitions of SR (status register) bit
offsets and will be use to reference PMC irqs.

Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>