arch: arm: socfpga: timer_s10: Override udelay for secure section

Override __udelay() as 'always inlined' function so that PSCI code
run in '__secure' section can call this delay function as well.

Signed-off-by: Chee Hong Ang <chee.hong.ang@intel.com>
Signed-off-by: Dinesh Maniyam <dinesh.maniyam@intel.com>
Reviewed-by: Tien Fong Chee <tien.fong.chee@intel.com>