NFC: dts: st21nfca: Document ese-present & uicc-present DTS property

On st21nfca, the mechanism to enable a secure element needs to add 2
properties in order manage the SWP line correctly.

Document ese-present and uicc-present properties.
Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

Documentation/devicetree/bindings/net/nfc/st21nfca.txt

@@ -11,6 +11,10 @@ Required properties:
 Optional SoC Specific Properties:
 - pinctrl-names: Contains only one value - "default".
 - pintctrl-0: Specifies the pin control groups used for this controller.
+- ese-present: Specifies that an ese is physically connected to the nfc
+controller.
+- uicc-present: Specifies that the uicc swp signal can be physically
+connected to the nfc controller.
 
 Example (for ARM-based BeagleBoard xM with ST21NFCA on I2C2):
 
@@ -29,5 +33,8 @@ Example (for ARM-based BeagleBoard xM with ST21NFCA on I2C2):
 		interrupts = <2 IRQ_TYPE_LEVEL_LOW>;
 
 		enable-gpios = <&gpio5 29 GPIO_ACTIVE_HIGH>;
+
+		ese-present;
+		uicc-present;
 	};
 };