configs/olimex_a64_olinuxino: bump to Linux kernel 5.15.7, u-boot 2021.10 and ATF v2.5

1) Now u-boot needs SCP environment variable specified that can point to
the or1k coprocessor firmware while if coprocessor is not used it must
be passed /dev/null as we do in this case.
2) We now use the u-boot-sunxi-with-spl.bin instead of u-boot.itb since
it's produced by u-boot anymore.
3) U-Boot 2021.10 requires python 3 and openssl so let's enable them.
4) Remove local patches for uboot and linux.
5) Remove global patches path from defconfig.

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>