arm64: tegra21: emc: Add seq rev. 21015

arm64: tegra21: emc: Add seq rev. 21015

Add the 21015 sequence to the list of known sequences. This required several
changes to the overall sequence such as removing the const qualifier on
the table structs (it does get modified in the 21015 rev. due to periodic
training.

Change-Id: I3d4412e73fd1f16d5da63e29c429fdb809a469fa
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: http://git-master/r/660448
(cherry picked from commit 0f6ff9dc4b111a904fc70da3ca78dc602ac91af5)
Reviewed-on: http://git-master/r/663392
Reviewed-by: Mitch Luban <mluban@nvidia.com>