runqemu: resize rootfs image to power of 2 for SD or pflash

runqemu: resize rootfs image to power of 2 for SD or pflash

QEMU requires that SD and pflash images are sized to be a power of 2
(e.g., 32M, 64M, etc).  So, if the image being used is not a power of 2
and it's being used for SD or pflash, increase it to the next power of 2
size via the truncate command.

This might not be an actual spec requirement, and is being investigated
in https://gitlab.com/qemu-project/qemu/-/issues/1754

Signed-off-by: Jon Mason <jon.mason@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>