plat/fvp: Support for extracting UART serial node info from DT

plat/fvp: Support for extracting UART serial node info from DT

This patch introduces the populate function which leverages
a new driver to extract base address and clk frequency properties
of the uart serial node from HW_CONFIG device tree.

This patch also introduces fdt helper API fdtw_translate_address()
which helps in performing address translation.

Change-Id: I053628065ebddbde0c9cb3aa93d838619f502ee3
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>