wic: Add 512 Byte alignment to --offset

wic: Add 512 Byte alignment to --offset

Allows the --offset argument to use the "s" or "S" suffix to specify
that it is reporting the number of 512 byte sectors.

This is required for some SoCs where the mask ROM looks for an item at a
sector that isn't aligned to a 1KB boundary.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>