base: Clean up redundant string functions and use C++11

This patch does a bit of housekeeping on the string helper functions
and relies on the C++11 standard library where possible. It also does
away with our custom string hash as an implementation is already part
of the standard library.

src/dev/uart8250.cc

@@ -36,7 +36,6 @@
 #include <vector>
 
 #include "base/inifile.hh"
-#include "base/str.hh"        // for to_number
 #include "base/trace.hh"
 #include "config/the_isa.hh"
 #include "debug/Uart.hh"