rtc: spear: drop uie_unsupported

Since commitc9f5c7e7a84f ("rtc: rtc-spear: Provide flag for no support of
UIE mode") which was in 2012, the core changed a lot and UIE are now
supported using regular alarms. Drop uie_unsupported now to reflect that.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://lore.kernel.org/r/20220309162301.61679-20-alexandre.belloni@bootlin.com