platform/chrome: chromeos_acpi: print hex string for ACPI_TYPE_BUFFER

`element->buffer.pointer` should be binary blob.  `%s` doesn't work
perfect for them.

Print hex string for ACPI_TYPE_BUFFER.  Also update the documentation
to reflect this.

Fixes: 0a4cad9c

 ("platform/chrome: Add ChromeOS ACPI device driver")
Cc: stable@vger.kernel.org
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20230803011245.3773756-1-tzungbi@kernel.org
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>