Describe the bug

(follow-up issue to #75125)

After merge of #75245, the chan_blen_transfer test now succeeds on STM32WB0 MCUs but fails on Nucleo-H743ZI.

Relevant test log extract:

===================================================================                                                                       
START - test_tst_dma1_m2m_chan0_burst16                                                                                                   
Preparing DMA Controller: Name=dmamux@58025800, Chan_ID=4, BURST_LEN=2                                                                    
Starting the transfer                                                                                                                     
E: invalid source address                                                                                                                 
E: cannot configure the dmamux. 

The invalid source address message is emitted here:

TL;DR: the DMA driver refuses the transfer because the source is not in SRAM4.

The regression comes from the fact that, beforehand, the .rodata and .bss segments of the test code could be relocated thanks to:

And indeed, the Kconfig for Nucleo-H743ZI makes use of this feature:

Before #75245, the test looked like this:

• tx_buff is static const and initialized, so it goes in .rodata and gets relocated
• rx_buff is static, not const, but uninitialized, so it goes in .bss and gets relocated
  After the patch, it now looks like this:
  

  zephyr/tests/drivers/dma/chan_blen_transfer/src/test_dma.c

  Lines 25 to 26 in 662b980

  	static __aligned(32) char tx_data[] = "It is harder to be kind than to be wise........";
  	static __aligned(32) char rx_data[RX_BUFF_SIZE] = { 0 };

• tx_buff is static, not const, and initialized, so it goes in .data and is not relocated
• rx_buff is static, not const, but uninitialized, so it goes in .bss and gets relocated

Expected behavior
Test should not fail.

Impact
Test breakage on Nucleo-H743ZI and potentially all boards with a Kconfig overlay setting CONFIG_DMA_LOOP_TRANSFER_RELOCATE_SECTION (i.e., mimxrt boards).