clk: samsung: exynos4: mark 'chipid' clock as CLK_IGNORE_UNUSED

clk: samsung: exynos4: mark 'chipid' clock as CLK_IGNORE_UNUSED

The ChipID IO region has it's own clock, which is being disabled while
scanning for unused clocks. It turned out that some CPU hotplug, CPU idle
or even SOC firmware code depends on the reads from that area. Fix the
mysterious hang caused by entering deep CPU idle state by ignoring the
'chipid' clock during unused clocks scan, as there are no direct clients
for it which will keep it enabled.

Fixes: 0a21e8c97c5c ("clk: exynos4: register clocks using common clock framework")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20200922124046.10496-1-m.szyprowski@samsung.com
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>