perf: Export perf_event_update_userpage

Export perf_event_update_userpage() so that PMU driver using them,
can be built as modules.

Change-Id: Ifde08970489272121c3098f6e502d2e628a03f39
Acked-by: Peter Zilstra <peterz@infradead.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Git-commit: 82975c46da8275a2a212cd94049bbef9bb961da2
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>