posix: sys/stat.h: format for coding style compliance

The original format of this file as imported from PicoLibC was not
compatible with Zephyr's coding stytle. This change fixes
compliance issues listed below:

- whitespace formatting
- block comment formatting
- named parameters

Introduction of new typedefs should be considered false-negatives
as these are existing standard POSIX types.

Signed-off-by: Chris Friedt <cfriedt@meta.com>