Qualcomm MSS QDSP6v5 Peripheral Image Loader

pil-qdsp6v5-mss is a peripheral image loader (PIL) driver. It is used for
loading QDSP6v5 (Hexagon) firmware images for modem subsystems into memory and
preparing the subsystem's processor to execute code. It's also responsible for
shutting down the processor when it's not needed.

Required properties:
- compatible:	      Must be "qcom,pil-q6v5-mss"
- reg:		      Pairs of physical base addresses and region sizes of
		      memory mapped registers.
- reg-names:	      Names of the bases for the above registers. "qdsp6_base",
		      "halt_base", "rmb_base", "restart_reg", and
		      "metadata_base" are expected.
- interrupts:         The modem watchdog interrupt
- vdd_mss-supply:     Reference to the regulator that supplies the processor.
- vdd_cx-supply:      Reference to the regulator that supplies the vdd_cx domain.
- vdd_mx-supply:      Reference to the regulator that supplies the memory rail.
- qcom,firmware-name: Base name of the firmware image. Ex. "mdsp"
- qcom,gpio-err-fatal: GPIO used by the modem to indicate error fatal to the apps.
- qcom,gpio-force-stop: GPIO used by the apps to force the modem to shutdown.

Optional properties:
- vdd_pll-supply:     Reference to the regulator that supplies the PLL's rail.
- qcom,vdd_pll:       Voltage to be set for the PLL's rail.
- reg-names:          "cxrail_bhs_reg" - control register for modem power
		      domain.
- qcom,is-loadable:   Boolean- Present if the image needs to be loaded.
- qcom,pil-self-auth: Boolean- True if authentication is required.

Example:
	qcom,mss@fc880000 {
		compatible = "qcom,pil-q6v5-mss";
		reg = <0xfc880000 0x100>,
		      <0xfd485000 0x400>,
		      <0xfc820000 0x020>,
		      <0xfc401680 0x004>,
		      <0x0d1f0000 0x4000>;
		reg-names = "qdsp6_base", "halt_base", "rmb_base",
			    "restart_reg", metadata_base";
		interrupts = <0 24 1>;
		vdd_mss-supply = <&pm8841_s3>;
		vdd_cx-supply = <&pm8841_s2>;
		vdd_mx-supply = <&pm8841_s1>;

		qcom,is-loadable;
		qcom,firmware-name = "mba";
		qcom,pil-self-auth;

		/* GPIO inputs from mss */
		gpio_err_fatal = <&smp2pgpio_ssr_smp2p_1_in 0 0>;

		/* GPIO output to mss */
		gpio_force_stop = <&smp2pgpio_ssr_smp2p_1_out 0 0>;
	};