clk: at91: sama7g5: add 5th divisor for mck0 layout and characteristics

This SoC has the 5th divisor for the mck0 master clock.
Adapt the characteristics accordingly.

Reported-by: Mihai Sain <mihai.sain@microchip.com>
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>