memory: tegra: Fix -Wunused-const-variable

Clang produces the following warning

drivers/memory/tegra/tegra124.c:36:28: warning: unused variable
'tegra124_mc_emem_regs' [-Wunused-const-variable]
static const unsigned long tegra124_mc_emem_regs[] = {
                           ^

The only usage of this variable is from within an ifdef.
It seems logical to move the variable into the ifdef as well.

Cc: clang-built-linux@googlegroups.com
Link: https://github.com/ClangBuiltLinux/linux/issues/526
Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>