drivers/i2c/generic: Add "compatible" property to _DSD

This change adds support for allowing devices to provide a
"compatible" property string that can be used when _HID is set to
PRP00001. This is used to allow Linux kernel drivers to match the
device to appropriate driver based on the OF-style compatible
string.

Reference:
https://www.kernel.org/doc/Documentation/acpi/enumeration.txt

BUG=b:129162037
TEST=Verified that atmel touchscreen gets enumerated correctly on
kohaku using PRP0001 and compatible string.

Change-Id: I8a306854c67ab2f056ea8774df46599ef0c55761
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34813
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Paul Fagerburg <pfagerburg@chromium.org>

src/drivers/i2c/generic/chip.h

@@ -28,6 +28,7 @@ struct drivers_i2c_generic_config {
 	const char *desc;	/* Device Description */
 	unsigned uid;		/* ACPI _UID */
 	enum i2c_speed speed;	/* Bus speed in Hz, default is I2C_SPEED_FAST */
+	const char *compat_string;	/* Compatible string for _HID=PRP0001 */
 	unsigned wake;		/* Wake GPE */
 	struct acpi_irq irq;	/* Interrupt */