log: discard non standard %e format

Prior this change was %e a valid format for printing error codes as
strings when identified. This change removes such support and replace
use of %e with use of standard format identifier and a error code
to string conversion function.

With this change, any standard printf-like format comply with
SCP-firmware traces implementation. fwk_status_str() helps traces to
get nice string identifiers for errors.

This change updates few impacted modules.

Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>