Remove deprecated IO return definitions ...

Patch 7e26fe1f deprecates IO specific return definitions in favour
of standard errno codes. This patch removes those definitions
and its usage from the IO framework, IO drivers and IO platform
layer. Following this patch, standard errno codes must be used
when checking the return value of an IO function.

Change-Id: Id6e0e9d0a7daf15a81ec598cf74de83d5768650f

Move IO storage source to drivers directory ...

Move the remaining IO storage source file (io_storage.c) from the
lib to the drivers directory. This requires that platform ports
explicitly add this file to the list of source files.

Also move the IO header files to a new sub-directory, include/io.

Change-Id: I862b1252a796b3bcac0d93e50b11e7fb2ded93d6