ANDROID: ktime: Fix ktime references

Upstream commit 2456e855 ("ktime: Get rid of the union") got
rid of ktime union, just kept ktime_t as simple typedef of type s64.
So remove ktime.tv64 references and use ktime directly instead.

Also include <linux/ktime.h> to declare ktime_t type.

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>