update to latest v5.4-rt kernel for sam9x35 SOC

[yosi yarchi]

   Hi

     I'm working currently with 5.4.41-linux4sam-2020.04-rt kernel on
     sam9x35 SOC. there are no updates for this kernel for long time
     (since 2020). at linux-stable-rt, however, there are lot of
     updates for v5.4 kernel. I want to update to latest v5.4 kernel. I
     thought to:

       1. take linux-stable-rt repository as my base
       2. add missing files from maintainers repository
git://git.kernel.org/pub/scm/linux/kernel/git/at91/linux.git
         repository (pointed by MAINTAINERS file).

       however, what about exist but less updated files? the file
         drivers/dma/at_hdmac.c, for example, exist at both
         repositories, but git log shows that there are much more
         updates at maintainers repository than to linux-stable-rt
         repository (even at specific date, Oct 25 2022, for example).

    my question is: what is the right way to update to latest 5.4-rt
     kernel on sam9x SOCs?

    With best regards
    Yosi Yarchi