feat(fvp): add mbedtls_asn1_get_len symbol in ROMlib

mbedtls_asn1_get_len() will be needed by the X.509 parser in an
upcoming patch.

Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
Change-Id: I14310c80033a1142a94c0c4b54d63331479b643d
1 file changed