docs(fvp): update fvp build time options

Add new fvp specific build time options. Specifically the below:

- INITRD_SIZE
- INITRD_PATH
- INITRD_BASE

Change-Id: Ieadf01fce7a0a0a8e9e7582d7b7e371b247207c2
Signed-off-by: Salman Nabi <salman.nabi@arm.com>
diff --git a/docs/plat/arm/fvp/fvp-build-options.rst b/docs/plat/arm/fvp/fvp-build-options.rst
index b0359fa..79dc0dc 100644
--- a/docs/plat/arm/fvp/fvp-build-options.rst
+++ b/docs/plat/arm/fvp/fvp-build-options.rst
@@ -46,6 +46,16 @@
    is ``0``, which means the redistributor pages of all CPU cores are marked
    as read and write.
 
+-  ``INITRD_SIZE`` : Enable the insertion of initrd properties to the device
+   tree blob at build time. Takes an initrd size value in hex format
+
+-  ``INITRD_PATH`` : Enable the insertion of initrd properties to the device tree
+   blob at build time. Takes a path to an initrd file. Can be used as an
+   alternative to ``INITRD_SIZE``. ``INITRD_SIZE`` takes precedence over
+   ``INITRD_PATH`` if both values are provided.
+
+-  ``INITRD_BASE`` : Provide the preloaded initrd base address in memory (hex format).
+
 --------------
 
-*Copyright (c) 2019-2024, Arm Limited. All rights reserved.*
+*Copyright (c) 2019-2025, Arm Limited. All rights reserved.*