ARM: at91: prepare common clk transition for sam9n12 SoC

This patch encloses sam9n12 old clk registration in
"#if defined(CONFIG_OLD_CLK_AT91) #endif" sections.

Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
ARM: at91/dt: define sam9n12 clocks

Define sam9n12 clocks and make use of them in peripheral definitions.

Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
ARM: at91/dt: define sam9n12ek crystal frequencies

Define sam9n12ek's main and slow crystal frequencies.

Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
ARM: at91: move sam9n12 SoC to the CCF

This patch removes the selection of AT91_USE_OLD_CLK when selecting
sam9n12 SoC support. This will automatically enable COMMON_CLK_AT91 option
and add support for at91 common clk implementation.

Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>