socfpga64: Do not define CONFIG_SYS_MEM_RESERVE_SECURE to 0

socfpga64: Do not define CONFIG_SYS_MEM_RESERVE_SECURE to 0

Based on the comment in socfpga_soc64_common.h, the intention is for
CONFIG_SYS_MEM_RESERVE_SECURE to be unused.  However, in the code we do:
...

and that will evaluate to true.  This leads to unwanted code being
compiled.  Further, as CONFIG_SYS_MEM_RESERVE_SECURE has not been
migrated to Kconfig, this leads to a mismatch in the size of gd
depending on if we have or have not also had <configs/BOARD.h> also
included yet.

Remove the define as it's not needed.

Cc: Siew Chin Lim <elly.siew.chin.lim@intel.com>
Cc: Chee Hong Ang <chee.hong.ang@intel.com>
Cc: Dalon Westergreen <dalon.westergreen@intel.com>
Signed-off-by: Tom Rini <trini@konsulko.com>