rtc: pl031: document struct pl031_vendor_data members

Document the range related members of struct pl031_vendor_data.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202503011015.SYvdddTc-lkp@intel.com/


Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250305221659.1153495-1-alexandre.belloni@bootlin.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>