This patch adds new at91 pll clock implementation using common clk framework.

The pll clock layout describe the PLLX register layout.
There are four pll clock layouts:
- at91rm9200
- at91sam9g20
- at91sam9g45
- sama5d3

PLL clocks are given characteristics:
- min/max clock source rate
- ranges of valid clock output rates
- values to set in out and icpll fields for each supported output range

These characteristics are checked during rate change to avoid
over/underclocking.

These characteristics are described in atmel's SoC datasheet in
"Electrical Characteristics" paragraph.

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>