feat(linux): Add LPM chapter for J742S2 SOC

J742S2 is variant of J784s4 soc, this SOC supports LPM mode
as well.
So Add LPM chapter for J742S2 SOC.

Signed-off-by: Udit Kumar <u-kumar1@ti.com>

Author: uditkumarti

configs/J742S2/J742S2_linux_toc.txt

@@ -88,6 +88,8 @@ linux/Foundational_Components_Kernel_LTP-DDT_Validation
 linux/Foundational_Components_Kernel_FAQs
 linux/Foundational_Components_Security
 linux/Foundational_Components/System_Security/Security_overview
+linux/Foundational_Components_Power_Management
+linux/Foundational_Components/Power_Management/pm_low_power_modes_socoff
 linux/Foundational_Components_Filesystem
 linux/Foundational_Components_Tools
 linux/Foundational_Components/Tools/Development_Tools
@@ -142,4 +144,4 @@ linux/How_to_Guides/Hardware_Setup_with_CCS/J742S2_EVM_Hardware_Setup
 linux/How_to_Guides/Target/How_To_Carve_Out_CMA
 linux/Documentation_Tarball
 
-linux/Demo_User_Guides/Chromium_Browser
+linux/Demo_User_Guides/Chromium_Browser