ion: change ion kernel map function to not take flags argument

Buffer flags are going to be specified at allocation time rather than
map time. This removes the flags argument from the ion kernel map
function.

Change-Id: I91589ca7b1ab142bb5ac8e6b0f4c06fa1305f23a
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>