mmc: loongson2: Unify the function prefixes for loongson2_mmc_pdata

mmc: loongson2: Unify the function prefixes for loongson2_mmc_pdata

The function prefixes for loongson2_mmc_pdata follow two naming
conventions: SoC-based and DMA-based.

First, DMA-based prefixes are the preferred choice, as they clearly
highlight differences, such as prepare_dma; however, for functions
related to SoC, such as reorder_cmd_data, it is agreed to use the
smallest SoC name as the fallback prefix, such as ls2k0500.

No functional change intended.

Suggested-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Link: https://lore.kernel.org/r/20250716064421.3823418-1-zhoubinbin@loongson.cn
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>