ARM: at91/dt: split sam9x5 peripheral definitions

This patch splits the sam9x5 peripheral definitions into:
- a common base for all sam9x5 SoCs (at91sam9x5.dtsi)
- several optional peripheral definitions which will be included by specific
  sam9x5 SoCs (at91sam9x5_'periph name'.dtsi)

This provides a better representation of the real hardware (drop unneeded
dt nodes) and avoids future peripheral id conflict (lcdc and isi both use
peripheral id 25).

Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>