px4-fmuv5: config fix stm32f7 max SD card speed

[simonegu]

In the stm32f7 the configuration variable for SD card with DMA changed from CONFIG_STM32_SDIO_DMA to CONFIG_STM32F7_SDMMC_DMA
the maximum clock speed of 16MHz can now be achieved.

Need validation. @bkueng or @davids5 I don't have a fmu-v5 board would be great if you could try out and validate the fix.

[bkueng]

Tested on FMUv5 with sd_bench:
Before:

nsh> sd_bench
INFO  [sd_bench] Using block size = 4096 bytes, sync=0
INFO  [sd_bench]
INFO  [sd_bench] Testing Sequential Write Speed...
INFO  [sd_bench]   Run  0:   491.05 KB/s, max write time: 13 ms (= 307.69 KB/s), fsync: 4 ms
INFO  [sd_bench]   Run  1:   486.63 KB/s, max write time: 12 ms (= 333.33 KB/s), fsync: 3 ms
INFO  [sd_bench]   Run  2:   484.07 KB/s, max write time: 14 ms (= 285.71 KB/s), fsync: 5 ms
INFO  [sd_bench]   Run  3:   488.85 KB/s, max write time: 11 ms (= 363.64 KB/s), fsync: 6 ms
INFO  [sd_bench]   Run  4:   485.28 KB/s, max write time: 12 ms (= 333.33 KB/s), fsync: 4 ms
INFO  [sd_bench]   Avg   :   487.18 KB/s

after:

INFO  [sd_bench] Using block size = 4096 bytes, sync=0
INFO  [sd_bench]
INFO  [sd_bench] Testing Sequential Write Speed...
INFO  [sd_bench]   Run  0:   500.21 KB/s, max write time: 12 ms (= 333.33 KB/s), fsync: 4 ms
INFO  [sd_bench]   Run  1:   500.81 KB/s, max write time: 12 ms (= 333.33 KB/s), fsync: 3 ms
INFO  [sd_bench]   Run  2:   489.55 KB/s, max write time: 17 ms (= 235.29 KB/s), fsync: 5 ms
INFO  [sd_bench]   Run  3:   494.92 KB/s, max write time: 11 ms (= 363.64 KB/s), fsync: 4 ms
INFO  [sd_bench]   Run  4:   501.11 KB/s, max write time: 12 ms (= 333.33 KB/s), fsync: 4 ms
INFO  [sd_bench]   Avg   :   497.32 KB/s

[LorenzMeier]

Many thanks!