at91: kernel: bump to 5.10

at91: kernel: bump to 5.10

Bump at91 targets to kernel v5.10. With this patches and files for
wb45n and wb50n were removed as they are now included in upstream
kernel. Along with:
- this the kernel config for sama5d2 and sam9x targets has been
  refreshed (with make kernel_menuconfig + save);
- CONFIG_ARCH_AT91 and specific sam9x SoCs (AT91RM9200, AT91SAM9,
  SAM9X60) has been enabled such that sam9x SoCs to be able to boot.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>