ARM: multi_v7_defconfig: add sama7g5 SoC

Add the Microchip SAMA7G5 ARM v7 Cortex-A7 based SoC to multi_v7_defconfig.
Also add it's clock timer, the PIT64B.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20210628120452.74408-4-eugen.hristev@microchip.com