Move platform_helpers.S to each platform's folder

In practice, all the functions in this file are platform-specific. It is
better to force all platforms to implement than having some sort of weak
function placeholder.

Porting guide updated.

Change-Id: I5beeeb10bec6fe5178b24503d6da8ca66074a8c6
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/docs/porting-guide.rst b/docs/porting-guide.rst
index 59d9dba..9c0812f 100644
--- a/docs/porting-guide.rst
+++ b/docs/porting-guide.rst
@@ -298,6 +298,47 @@
 
 This function initializes the ARM Generic Interrupt Controller (GIC).
 
+Function : platform_get_core_pos() [mandatory]
+``````````````````````````````````````````````
+
+::
+
+    Argument : u_register_t
+    Return   : unsigned int
+
+This function returns a linear core ID from a MPID.
+
+Function : plat_crash_console_init() [mandatory]
+````````````````````````````````````````````````
+
+::
+
+    Argument : void
+    Return   : int
+
+This function initializes a platform-specific console for crash reporting.
+
+Function : plat_crash_console_putc() [mandatory]
+````````````````````````````````````````````````
+
+::
+
+    Argument : int
+    Return   : int
+
+This function prints a character on the platform-specific crash console.
+
+Function : plat_crash_console_flush() [mandatory]
+`````````````````````````````````````````````````
+
+::
+
+    Argument : void
+    Return   : int
+
+This function waits until all the characters of the platform-specific crash
+console have been actually printed.
+
 Optional modifications
 ----------------------
 
@@ -350,17 +391,6 @@
 generate a watchdog timeout interrupt. This interrupt remains deliberately
 unserviced, which eventually asserts the reset signal.
 
-Function : tftf_platform_setup()
-````````````````````````````````
-
-::
-
-    Argument : void
-    Return   : void
-
-Setup code for platform hardware. The default implementation initializes the IO
-and GIC.
-
 Storage abstraction layer
 -------------------------