platform/x86: thinkpad_acpi: Simplify thermal mode checking

platform/x86: thinkpad_acpi: Simplify thermal mode checking

Add a thermal_read_mode_check helper to make the code
simpler during init. This helps particularly when the new
TPACPI_THERMAL_TPEC_12 mode is added in the next patch.

Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Vishnu Sankar <vishnuocv@gmail.com>
Link: https://lore.kernel.org/r/20240215134102.25118-1-vishnuocv@gmail.com
[ij: Reflowed the comment to 80 cols, multiline if braces, added __init.]
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>