Fix build with clang in C++11 mode

This removes the deprecated register keyword in many places, fixes one
instance of passing '\0' where a char* is expected, and 2 switch type
narrowing issues.

Change-Id: Ie265ac26ff6a61267ad6406dfe237226d97ca9ac
Signed-off-by: Bernhard Rosenkränzer <Bernhard.Rosenkranzer@linaro.org>