doc: Fix plat_sdei_validate_entry_point() documentation

Document the second argument of the function.
Minor rewording.

Change-Id: I190794b8cc74c99db4cfe6efc225217c32dd0774
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>

docs/getting_started/porting-guide.rst

@@ -1956,23 +1956,27 @@ be higher than Normal |SDEI| priority.
 Functions
 .........
 
-Function: int plat_sdei_validate_entry_point(uintptr_t ep) [optional]
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Function: int plat_sdei_validate_entry_point() [optional]
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 ::
 
-  Argument: uintptr_t
+  Argument: uintptr_t ep, unsigned int client_mode
   Return: int
 
-This function validates the address of client entry points provided for both
-event registration and *Complete and Resume* |SDEI| calls. The function
-takes one argument, which is the address of the handler the |SDEI| client
-requested to register. The function must return ``0`` for successful validation,
-or ``-1`` upon failure.
+This function validates the entry point address of the event handler provided by
+the client for both event registration and *Complete and Resume* |SDEI| calls.
+The function ensures that the address is valid in the client translation regime.
+
+The second argument is the exception level that the client is executing in. It
+can be Non-Secure EL1 or Non-Secure EL2.
+
+The function must return ``0`` for successful validation, or ``-1`` upon failure.
 
 The default implementation always returns ``0``. On Arm platforms, this function
-is implemented to translate the entry point to physical address, and further to
-ensure that the address is located in Non-secure DRAM.
+translates the entry point address within the client translation regime and
+further ensures that the resulting physical address is located in Non-secure
+DRAM.
 
 Function: void plat_sdei_handle_masked_trigger(uint64_t mpidr, unsigned int intr) [optional]
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^