efi_loader: correctly implement 100ns conversion

In efi_set_timer we receive the trigger time in intervals of 100 ns.
We should convert it to intervals of 1000 ns by 64bit division.

The patch supplies function efi_div10 that uses multiplication to
implement the missing 64 bit division.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>