feat(linux): Add initial performance guide for AM64X 12.00.00 release

Add the initial Linux & RT Linux performance guide for 12.00.00 release
for AM64X.

Note that the following sections are pending updates.
- ETHERNET
- RT CYCLIC
- IPC
- Multibench

Signed-off-by: Judith Mendez <jm@ti.com>

Author: jmenti

source/devices/AM64X/linux/Linux_Performance_Guide.rst

@@ -1,5 +1,5 @@
 ====================================
- Linux 11.02.08.02 Performance Guide
+ Linux 12.00.00 Performance Guide
 ====================================
 
 .. rubric::  **Read This First**