arm: Properly support 64-bit read/write

Several places were incorrectly casting 64 bit types to
32 bit types. Cast to the appropriate value. Also, actually
assign the value we are attempting to write to the correct
register. This way, we actually write the value we want
instead of whatever happens to be in r2.

Change-Id: Ica0b40b9ea5916f6dc11c011d8875cdb59e2feba
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>