RM 6661: Revert "RM 6641: Temporary implementation of dma_alloc_coherent() on STM32H7 SOM"

[av-dyachenko]

Design

This hack is not required as soon as the appropriate DMA memory pool is defined in the device tree:

        reserved-memory {
                ...
                /* The DMA memory pool is needed by Ethernet driver
                   to allocate buffer descriptors using the standard DMA API */
                dmapool@d0300000 {
                        compatible = "shared-dma-pool";
                        reg = <0xd0300000 0x100000>;
                        no-map;
                        linux,dma-default;
                };

Test

Refer to the U-Boot PR: https://gitlab.com/emcraft/STM32H7/u-boot-upstream/-/merge_requests/6