fix(configs): J721S2: Remove PCIe Backplane Documentation

The J721S2 EVM has only one functional PCIe slot (PCIe1), the second
PCIe connector is unused. The PCIe backplane functionality requires at
least two PCIe endpoints. Therefore, PCIe backplane cannot be used on
this platform.

Signed-off-by: Aksh Garg <a-garg7@ti.com>

Author: AkshGarg-19

configs/J721S2/J721S2_linux_toc.txt

@@ -69,7 +69,7 @@ linux/Foundational_Components/Kernel/Kernel_Drivers/Network/CPSW-CBS
 linux/Foundational_Components/Kernel/Kernel_Drivers/Network/CPSW-IET
 linux/Foundational_Components/Kernel/Kernel_Drivers/Network/CPSW-TSN-Tuning
 linux/Foundational_Components/Kernel/Kernel_Drivers/PCIe/PCIe_End_Point
-linux/Foundational_Components/Kernel/Kernel_Drivers/PCIe/PCIe_Backplane
+#linux/Foundational_Components/Kernel/Kernel_Drivers/PCIe/PCIe_Backplane
 linux/Foundational_Components/Kernel/Kernel_Drivers/PCIe/PCIe_Root_Complex
 linux/Foundational_Components/Kernel/Kernel_Drivers/PMIC/pmic_tps6594
 linux/Foundational_Components_Power_Management