arm: exynos: Wait till ADC stabilizes before checking Odroid HC1 revision

arm: exynos: Wait till ADC stabilizes before checking Odroid HC1 revision

Fix detection of Odroid HC1 (Exynos5422) after reboot if kernel disabled
the LDO4/VDD_ADC regulator.

The LDO4 supplies both ADC block and the ADC input AIN9.  Voltage on
AIN9 will rise slowly, so use delay of 5 milliseconds instead of
timers-based loop to wait for voltage stabilization.

First reads on Odroid HC1 return 305, 1207, 1297 and finally 1308
(reference value is 1309).

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Tested-by: Anand Moon <linux.amoon@gmail.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>