ion: Update ION_SECURE and ION_FORCE_CONTIGUOUS flags

Rename ION_SECURE and ION_FORCE CONTIGUOUS to ION_FLAG_SECURE
and ION_FLAG_FORCE_CONTIGUOUS respectively, but leave the old
ones intact for backwards compatability.

Change-Id: I31ee3088ed202f60e14c10ac66d775c64c01c4e3
Signed-off-by: Adrian Alexei <aalexei@codeaurora.org>