STM32F7 disable d-cache as a precaution (#11374)

 - see 1259864 Data corruption in a sequence of Write-Through stores and loads
 - if we can be certain this sequence won't occur in PX4 then the d-cache will be re-enabled

boards/av/x-v1/nuttx-config/nsh/defconfig

@@ -162,8 +162,7 @@ CONFIG_ARMV7M_HAVE_DCACHE=y
 CONFIG_ARMV7M_USEBASEPRI=y
 CONFIG_ARMV7M_BASEPRI_WAR=y
 CONFIG_ARMV7M_ICACHE=y
-CONFIG_ARMV7M_DCACHE=y
-CONFIG_ARMV7M_DCACHE_WRITETHROUGH=y
+# CONFIG_ARMV7M_DCACHE is not set
 CONFIG_ARMV7M_HAVE_ITCM=y
 CONFIG_ARMV7M_HAVE_DTCM=y
 # CONFIG_ARMV7M_ITCM is not set