This patch adds support for authentication of both plain
text and encrypted binaries. A new SECDEV package is needed
to enable encryption of binaries by default for AM3x.

The ROM authentication API detects encrypted images at
runtime and automatically decrypts the image if the
signature verification passes.

Addition of encryption on AM3x results in a change in the
image format. On AM4x, AM5x and, on AM3x devices signing
clear test images, the signature is appended to the end of the
binary.

On AM3x, when the SECDEV package is used to create signed
and encrypted images, the signature is added as a header
to the start of the binary. So the binary size calculation
has been updated to reflect this change.

The signing tools and encrypted image format for AM3x
cannot be changed to behave like AM4x and AM5x to
maintain backward compatibility with older Sitara
M-Shield releases.

Signed-off-by: Madan Srinivas <madans@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>