clk: at91: sama7g5: do not allow cpu pll to go higher than 1GHz

clk: at91: sama7g5: do not allow cpu pll to go higher than 1GHz

Since CPU PLL feeds both CPU clock and MCK0, MCK0 cannot go higher
than 200MHz and MCK0 maximum prescaller is 5 limit the CPU PLL at
1GHz to avoid MCK0 overclocking while CPU PLL is changed by DVFS.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/1605800597-16720-10-git-send-email-claudiu.beznea@microchip.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>