dts: arm: atmel: samd5x: Fix CPU compatible

The SAM D5x and E5x series SoCs include the "Cortex-M4F" core, not the
FPU-less "Cortex-M4" core.

This commit fixes the incorrect CPU compatible for the SAM D5x and E5x
SoCs (note that this file is included by `same5x.dtsi`, which is used
as the base device tree header for the SAM E5x series).

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>