xilinx: zynq: Change types from u32 to uint32_t

Change parameter type to avoid compilation error:
In file included from ./tools/../lib/rsa/rsa-verify.c:23:0,
                 from tools/lib/rsa/rsa-verify.c:1:
include/u-boot/rsa-mod-exp.h:69:18: error: unknown type name ‘u32’; did you mean ‘__u32’?
 int zynq_pow_mod(u32 *keyptr, u32 *inout);
                  ^~~
                  __u32
include/u-boot/rsa-mod-exp.h:69:31: error: unknown type name ‘u32’; did you mean ‘__u32’?
 int zynq_pow_mod(u32 *keyptr, u32 *inout);
                               ^~~
                               __u32

Fixes: 37e3a36a ("xilinx: zynq: Add support to secure images")
Signed-off-by: Michal Simek <michal.simek@xilinx.com>