After enabling a module, SW has to wait on IDLEST bit
until it is Fully functional. This wait is missing for UART module
and there is a immediate access of UART registers after this. So there
is a chance of hang on this module( This can happen when we are running
from MPU SRAM). So waiting for IDLEST bit.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>