cc3200: Make use of mem.h file in soc dtsi file.

This in preparation for adding a cc3220sf DTS file, which
has a different address for sram0 than the cc3200.

Also moved baud-rate out of soc dtsi file to board dts.

Jira: JEP-1958

Change-Id: I641452c0a8a6d1ad4424e132d6ef2de71d8545b4
Signed-off-by: Gil Pitney <gil.pitney@linaro.org>