zephyr: stm32h7 tests: spi_loopback fails due to mem_region

Describe the bug The tescase tests/drivers/spi/spi_loopback/ now fails when ruuning on a stm32h7 target

After the merge of https://github.com/zephyrproject-rtos/zephyr/pull/57786 There is a mem region definition missing to PASS the testcase

To Reproduce Steps to reproduce the behavior:

1. west build -p auto -b nucleo_h753zi tests/drivers/spi/spi_loopback/
2. west flash
3. connect D11 <–> D12 on the nucleo 144 target board
4. See error

Expected behavior test PASSED

PASS - test_spi_loopback in 0.049 seconds
===================================================================
TESTSUITE spi_loopback succeeded

------ TESTSUITE SUMMARY START ------

SUITE PASS - 100.00% [spi_loopback]: pass = 1, fail = 0, skip = 0, total = 1 dus
 - PASS - [spi_loopback.test_spi_loopback] duration = 0.049 seconds

------ TESTSUITE SUMMARY END -----

Impact CI failure

Logs and console output

*** Booting Zephyr OS build zephyr-v3.4.0-1785-gdfeb2d902756 ***                
Running TESTSUITE spi_loopback                                                  
===================================================================             
START - test_spi_loopback                                                       
I: SPI test on buffers TX/RX 0x240001b5/0x240009ce                              
I: SPI test slow config                                                         
I: Start complete multiple                                                      
E: Code -14                                                                     

    Assertion failed at WEST_TOPDIR/zephyr/tests/drivers/spi/spi_loopback/src/spi.c:111: spi_complete_multiple: (ret is true)
SPI transceive failed                                                                                                                                                                              
 FAIL - test_spi_loopback in 0.024 seconds                                      
===================================================================             
TESTSUITE spi_loopback failed.  

Environment (please complete the following information):

• OS: Ubuntu
• Toolchain 0.16.1
• Commit SHA : dfeb2d902756863c7bb1ae47c0996be678669f20