boards: convert to using newly introduced integer sized types

Convert code to use u{8,16,32,64}_t and s{8,16,32,64}_t instead of C99
integer types.

Jira: ZEP-2051

Change-Id: I27d51c316144251939b20cfa6787ff7ab8035fe6
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>