This patch adds necessary updates for building and running Trusted
Firmware for AArch32 to user-guide.md. The instructions for running
on both `FVP_Base_AEMv8A-AEMv8A` in AArch32 mode and
`FVP_Base_Cortex-A32x4` models are added. The device tree files for
AArch32 Linux kernel are also added in the `fdts` folder.

Change-Id: I0023b6b03e05f32637cb5765fdeda8c8df2d0d3e