anchao 1c91aec6ae tools/ and fs/procfs: Simplify .version file generation
1.merge CONFIG_GIT_REVISION_STR into CONFIG_VERSION_BUILD
2.merge gen_getrev.sh into version.sh
3.generate version number if needed

Here is a sample output:
nsh> uname -a
NuttX  8.2 59fd8e12d3-dirty Dec 12 2019 15:48:00 sim sim
nsh> cat /proc/version
NuttX version 8.2 59fd8e12d3-dirty Dec 12 2019 15:48:01
2019-12-12 11:17:11 -06:00
..
2019-01-09 14:26:51 -06:00