configs/atmel: bump at91 defconfigs to at91bootstrap 3.8.10
Bump at91sam9260ek, at91sam9g20, at91sam9g45m10ek, and at91sam9rlek to
at91bootstrap 3.8.10.
at91bootstrap 3.8.10 is required to support gcc7.
Signed-off-by: Joshua Henderson <joshua.henderson@microchip.com>
Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>