kernel: config cleanups for 5.8+

Integrating the following configuration tweaks to fixup warnings and
remove obselete configs for 5.8+:

   84377c2c723 features: rename INTEL_PMC_IPC to MFD_INTEL_PMC_BXT
   89b30487d09 features/inline: remove
   0d357ccb3f3 intel-tco: switch ITCO_WDT to loadable module
   0baed75c082 bsp: Drop the stale USB_MUSB_AM335X_CHILD

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>