[nrf fromtree] boot: bootutil: Add TLV for size of compressed but decrypted image

This TLV is needed in order to know what the data length
provided to the decompression system is to remove the padding
that is a resultant of the encryption block size

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
(cherry picked from commit 4bda587)
(cherry picked from commit bc8d277)
Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>

Author: nordicjm

boot/bootutil/include/bootutil/image.h

@@ -124,6 +124,7 @@ struct flash_area;
                                             * the format and size of the raw slot (compressed)
                                             * signature
                                             */
+#define IMAGE_TLV_COMP_DEC_SIZE     0x73   /* Compressed decrypted image size */
 					   /*
 					    * vendor reserved TLVs at xxA0-xxFF,
 					    * where xx denotes the upper byte