TSP: Fix GCC 11.0.0 compilation error.

TSP: Fix GCC 11.0.0 compilation error.

This patch fixes the following compilation error
reported by aarch64-none-elf-gcc 11.0.0:

bl32/tsp/tsp_main.c: In function 'tsp_smc_handler':
bl32/tsp/tsp_main.c:393:9: error: 'tsp_get_magic'
 accessing 32 bytes in a region of size 16
 [-Werror=stringop-overflow=]
  393 |         tsp_get_magic(service_args);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~
bl32/tsp/tsp_main.c:393:9: note: referencing argument 1
 of type 'uint64_t *' {aka 'long long unsigned int *'}
In file included from bl32/tsp/tsp_main.c:19:
bl32/tsp/tsp_private.h:64:6: note: in a call to function 'tsp_get_magic'
   64 | void tsp_get_magic(uint64_t args[4]);
      |      ^~~~~~~~~~~~~

by changing declaration of tsp_get_magic function from
void tsp_get_magic(uint64_t args[4]);
to
uint128_t tsp_get_magic(void);
which returns arguments directly in x0 and x1 registers.

In bl32\tsp\tsp_main.c the current tsp_smc_handler()
implementation calls tsp_get_magic(service_args);
, where service_args array is declared as
uint64_t service_args[2];
and tsp_get_magic() in bl32\tsp\aarch64\tsp_request.S
copies only 2 registers in output buffer:
	/* Store returned arguments to the array */
	stp	x0, x1, [x4, #0]

Change-Id: Ib34759fc5d7bb803e6c734540d91ea278270b330
Signed-off-by: Alexei Fedorov <Alexei.Fedorov@arm.com>