MIPS: DTS: Add base device tree for Pistachio SoC

Add support for the base Device Tree for Imagination Technologies'
Pistachio SoC.

This commit supports the following peripherals:

 * Clocks
 * Pinctrl and GPIO
 * UART
 * SPI
 * I2C
 * PWM
 * ADC
 * Watchdog
 * Ethernet
 * MMC
 * DMA engine
 * Crypto
 * I2S
 * SPDIF
 * Internal DAC
 * Timer
 * USB
 * IR
 * Interrupt Controller

Signed-off-by: Rahul Bedarkar <rahul.bedarkar@imgtec.com>
Acked-by: James Hartley <james.hartley@imgtec.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/14393/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>