thermal: ti-bandgap: Add support for temperature sensor

The dra7xx series of SOCs contain a temperature sensor and an
associated analog-to-digital converter (ADC) which produces
an output which is proportional to the SOC temperature.
Add support for this temperature sensor.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

doc/device-tree-bindings/thermal/ti_soc_thermal.txt

@@ -0,0 +1,35 @@
+* Texas Instrument dra7xx SCM bandgap bindings
+
+In the System Control Module, SoC supplies a voltage reference
+and a temperature sensor feature that are gathered in the band
+gap voltage and temperature sensor (VBGAPTS) module. The band
+gap provides current and voltage reference for its internal
+circuits and other analog IP blocks. The analog-to-digital
+converter (ADC) produces an output value that is proportional
+to the silicon temperature.
+
+Required properties:
+- compatible : Should be:
+  - "ti,dra752-bandgap"
+- interrupts : this entry should indicate which interrupt line
+the talert signal is routed to;
+- regs : this is specific to each bandgap version, because
+the mapping may change from soc to soc, apart from depending
+on available features.
+
+Optional:
+- gpios : this entry should be used to inform which GPIO
+line the tshut signal is routed to. The informed GPIO will
+be treated as an IRQ;
+
+Example:
+bandgap {
+	reg = <0x4a0021e0 0xc
+		0x4a00232c 0xc
+		0x4a002380 0x2c
+		0x4a0023C0 0x3c
+		0x4a002564 0x8
+		0x4a002574 0x50>;
+	compatible = "ti,dra752-bandgap";
+	interrupts = <0 126 4>; /* talert */
+};