nanopi_m1{, _plus}_defconfig: U-Boot needs pylibfdt

nanopi_m1 and nanopi_m1_plus are sunxi boards that need pylibfdt in
U-Boot.

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/27873655
https://gitlab.com/buildroot.org/buildroot/-/jobs/27873656



Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Cc: Peter Korsgaard <peter@korsgaard.com>
Cc: Chakra Divi <2chakrass@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>