configs: am64x_evm_*_defconfig: Enable config to support gpt and FDT library overlay

Enable config to support gpt command on AM642 evm/sk and enable config for
FDT library overlay support

Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Link: https://lore.kernel.org/r/20210726152807.22991-7-a-govindraju@ti.com