time: Cleanup old CONFIG_GENERIC_TIME references that snuck in

Awhile back I removed all the CONFIG_GENERIC_TIME referecnes as
the last of the non-GENERIC_TIME arches were converted.

However, due to the functionality being important and around for
awhile, there apparently were some out of tree hardware enablement
patches that used it and have since been merged.

This patch removes the remaining instances of GENERIC_TIME.

Singed-off-by: John Stultz <john.stultz@linaro.org>