Update versions of dependencies in user-guide.md

Update versions of dependencies in user-guide.md

1. Update user-guide.md with the latest versions of dependent
components required by the tested configurations of ARM Trusted
Firmware. This includes the tested versions of Fixed Virtual
Platforms (FVPs), toolchain, EFI Development Kit 2(EDK2),
Linux kernel and Linux file system.

2. Remove the instructions to configure the Cortex Base FVP
with the legacy GICv2 memory map as this is no longer supported
since version 5.3 of the Base FVPs.

3. General tidyup of "Using the software" section.

Change-Id: If8264cd29036b59dc5ff435b5f8b1d072dd36ef0