arm: mvebu: Make serdes setup on Armada XP less noisy

arm: mvebu: Make serdes setup on Armada XP less noisy

Change some of the PEX configuration output lines from always output to
only ouput upon specific debug enabling.

This changes the SPL output from:

U-Boot SPL 2016.01-rc2-00037-g9353a7f (Dec 10 2015 - 10:27:42)
High speed PHY - Version: 2.1.5 (COM-PHY-V20)
Update Device ID PEX0782611ab
Update Device ID PEX1782611ab
Update Device ID PEX2782611ab
Update Device ID PEX3782611ab
Update Device ID PEX8782611ab
Update PEX Device ID 0x78260
High speed PHY - Ended Successfully
DDR3 Training Sequence - Ver 5.7.4
DDR3 Training Sequence - Ended Successfully

to:

U-Boot SPL 2016.01-rc2-00037-g9353a7f-dirty (Dec 10 2015 - 10:32:04)
High speed PHY - Version: 2.1.5 (COM-PHY-V20)
High speed PHY - Ended Successfully
DDR3 Training Sequence - Ver 5.7.4
DDR3 Training Sequence - Ended Successfully

Resulting in a little faster bootup time.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>