Tegra210: skip past sc7entry-fw signature header

This patch skips past the signature header added to the sc7entry-fw
binary by the previous level bootloader. Currently, the size of
the header is 1KB, so adjust the start address and the binary size
at the time of copy.

Change-Id: Id0494548009749035846d54df417a960c640c8f9
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>