ion: add kernel support to get buffer flags

Allow ION kernel clients to get an ion buffer's flags.
This will allow ION clients to be able to determine if a buffer
is cached, uncached, secure ect.

Change-Id: I5460478e69f28e74906fd298f57dabd9e62c1e1f
Signed-off-by: Liam Mark <lmark@codeaurora.org>