Parametrize baudrate and UART clock during console_init()

Parametrize baudrate and UART clock during console_init()

This patch adds baud rate and UART clock frequency as parameters
to the pl011 driver api console_init(). This allows each platform
to specify UART clock and baud rate according to their specific
hardware implementation.

Fixes ARM-software/tf-issues#215

Change-Id: Id13eef70a1c530e709b34dd1e6eb84db0797ced2