backlight: ktd253: Stabilize backlight

Remove interrupt disablement during backlight setting. It is
way to dangerous and makes platforms instable by having it
miss vblank IRQs leading to the graphics derailing.

The code is using ndelay() which is not available on
platforms such as ARM and will result in 32 * udelay(1)
which is substantial.

Add some code to detect if an interrupt occurs during the
tight loop and in that case just redo it from the top.

Fixes: 5317f37e ("backlight: Add Kinetic KTD253 backlight driver")
Cc: Stephan Gerhold <stephan@gerhold.net>
Reported-by:  <newbyte@disroot.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>