Introduce utils_parse_time_suffix

This function is based on utils_parse_size_suffix, but is to parse
(relatively short) time suffixes. It returns the time in microseconds.
So far, it supports:

 - u/us: microseconds, x1, same as no suffix
 - m/ms: milliseconds, x1 000
 - s: seconds, x1 000 000

 For example:

 - 32u becomes 32
 - 32us becomes 32
 - 32m becomes 32 000
 - 32ms becomes 32 000
 - 32s becomes 32 000 000

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>