Fix broken links to various sections across docs

These broken links were found with the help of this command:
$> sphinx-build -M linkcheck . build

A sample broken link is reported as follows:
(line   80) -local-   firmware-design.rst#secure-el1-payloads-and-dispatchers

Change-Id: I5dcefdd4b8040908658115647e957f6c2c5da7c2
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
diff --git a/docs/getting_started/porting-guide.rst b/docs/getting_started/porting-guide.rst
index 7aaeae2..6b8bbc6 100644
--- a/docs/getting_started/porting-guide.rst
+++ b/docs/getting_started/porting-guide.rst
@@ -2482,9 +2482,7 @@
 ``FVP_USE_GIC_DRIVER`` (See :ref:`build_options_arm_fvp_platform` for more
 details).
 
-See also: `Interrupt Controller Abstraction APIs`__.
-
-.. __: ../design/platform-interrupt-controller-API.rst
+See also: :ref:`Interrupt Controller Abstraction APIs<Platform Interrupt Controller API>`.
 
 Function : plat_interrupt_type_to_line() [mandatory]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -2609,9 +2607,7 @@
 the highest pending interrupt has begun. It should return the raw, unmodified
 value obtained from the interrupt controller when acknowledging an interrupt.
 The actual interrupt number shall be extracted from this raw value using the API
-`plat_ic_get_interrupt_id()`__.
-
-.. __: ../design/platform-interrupt-controller-API.rst#function-unsigned-int-plat-ic-get-interrupt-id-unsigned-int-raw-optional
+`plat_ic_get_interrupt_id()<plat_ic_get_interrupt_id>`.
 
 This function in Arm standard platforms using GICv2, reads the *Interrupt
 Acknowledge Register* (``GICC_IAR``). This changes the state of the highest