TF-A: Add support for Measured Boot driver in BL1 and BL2

This patch adds support for Measured Boot driver functionality
in BL1 and BL2 code.

Change-Id: I7239a94c3e32b0a3e9e73768a0140e0b52ab0361
Signed-off-by: Alexei Fedorov <Alexei.Fedorov@arm.com>