device: Add helper function is_devfn_enabled()

is_devfn_enabled() function helps to check if a device
is enabled based on given device function number. This
function internally called is_dev_enabled() to check
device state.

Change-Id: I6aeba0da05b13b70155a991f69a6abf7eb48a78c
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55278
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/device/device_const.c

@@ -397,3 +397,9 @@ bool is_dev_enabled(const struct device *dev)
 		return false;
 	return dev->enabled;
 }
+
+bool is_devfn_enabled(unsigned int devfn)
+{
+	const struct device *dev = pcidev_path_on_root(devfn);
+	return is_dev_enabled(dev);
+}