staging: pi433: add missing register contants

add missing register constants present in RFM69 and/or RFM69HW so that
we don't need to hardcode values when referencing them.

this patch adds REG_TESTLNA, REG_TESTAFC constants

Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
Link: https://lore.kernel.org/r/20220124042636.GA7962@mail.google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>