ACPI / osi: Cleanup coding style issues before creating a separate OSI source file

This patch performs necessary cleanups before moving OSI support to
another file.

 1. Change printk into pr_xxx
 2. Do not initialize values to 0
 3. Do not append additional "return" at the end of the function
 4. Remove useless comments which may easily break line breaking rule

After fixing the coding style issues, rename functions to make them looking
like acpi_osi_xxx.

No functional changes.

Tested-by: Lukas Wunner <lukas@wunner.de>
Tested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>