bootutil: Conditionally include crypto/common.h

This is an Mbed TLS header including mbedtls/version.h
which can cause build errors when the PSA Crypto backend
is used with the TF-PSA-Crypto library.

Do not include crypto/common.h for builds with PSA Crypto.

Change-Id: I341846965de26ae2d63f1d6c163cd7a9025d6a1c
Signed-off-by: David Vincze <david.vincze@arm.com>