docs(prerequisites): update software and libraries prerequisites

Update to use the following software:

- mbed TLS == 3.4.0
- (DTC) >= 1.4.7
- Ubuntu 22.04 for builds.

Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
Change-Id: I384aab4dfee9cae9453eebf4091abe82ef9ccfaa
diff --git a/docs/getting_started/prerequisites.rst b/docs/getting_started/prerequisites.rst
index a3f8cc8..f4c3c28 100644
--- a/docs/getting_started/prerequisites.rst
+++ b/docs/getting_started/prerequisites.rst
@@ -14,7 +14,7 @@
 |TF-A| can be built using either a Linux or a Windows machine as the build host.
 
 A relatively recent Linux distribution is recommended for building |TF-A|. We
-have performed tests using Ubuntu 20.04 LTS (64-bit) but other distributions
+have performed tests using Ubuntu 22.04 LTS (64-bit) but other distributions
 should also work fine as a base, provided that the necessary tools and libraries
 can be installed.
 
@@ -77,11 +77,11 @@
 The following libraries are required for Trusted Board Boot and Measured Boot
 support:
 
-- mbed TLS == 2.28.1 (tag: ``mbedtls-2.28.1``)
+- mbed TLS == 3.4.0 (tag: ``mbedtls-3.4.0``)
 
 These tools are optional:
 
-- Device Tree Compiler (DTC) >= 1.4.6
+- Device Tree Compiler (DTC) >= 1.4.7
 
    Needed if you want to rebuild the provided Flattened Device Tree (FDT)
    source files (``.dts`` files). DTC is available for Linux through the package