board/lsi : set tref_enable during DDR controller init

Signed-off-by: Gary McGee <gary.mcgee@lsi.com>
Merge branch 'lsi-v2013.01.01' of github.com:lsigithub/lsi_axxia_uboot into lsi-v2013.01.01
Merge branch 'lsi-v2013.01.01' of github.com:lsigithub/lsi_axxia_uboot into lsi-v2013.01.01