ChibiOS: disable DMA on I2C on F7 and H7 by default

this was already done on many (most?) boards, and greatly reduces DMA
sharing which improves performance of UARTs. This changes the default
to no DMA on I2C

libraries/AP_HAL_ChibiOS/hwdef/common/stm32f47_mcuconf.h

@@ -579,3 +579,10 @@
 
 // limit ISR count per byte
 #define STM32_I2C_ISR_LIMIT                 6
+
+#if defined(STM32F7xx_MCUCONF)
+// disable DMA on I2C by default on F7
+#ifndef STM32_I2C_USE_DMA
+#define STM32_I2C_USE_DMA FALSE
+#endif
+#endif

libraries/AP_HAL_ChibiOS/hwdef/common/stm32h7_mcuconf.h

@@ -626,3 +626,7 @@
 #define STM32_SPI_SPI6_TX_BDMA_STREAM 5
 #define STM32_ADC_ADC3_BDMA_STREAM 7
 
+// disable DMA on I2C by default on H7
+#ifndef STM32_I2C_USE_DMA
+#define STM32_I2C_USE_DMA FALSE
+#endif

libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py

@@ -151,7 +151,7 @@ def get_mcu_lib(mcu):
 
 def setup_mcu_type_defaults():
     '''setup defaults for given mcu type'''
-    global pincount, ports, portmap, vtypes, mcu_type
+    global pincount, ports, portmap, vtypes, mcu_type, dma_exclude_pattern
     lib = get_mcu_lib(mcu_type)
     if hasattr(lib, 'pincount'):
         pincount = lib.pincount
@@ -166,6 +166,9 @@ def setup_mcu_type_defaults():
         for pin in range(pincount[port]):
             portmap[port].append(generic_pin(port, pin, None, default_gpio[0], default_gpio[1:]))
 
+    if mcu_series.startswith("STM32H7") or mcu_series.startswith("STM32F7"):
+        # default DMA off on I2C for H7, we're much better off reducing DMA sharing
+        dma_exclude_pattern = ['I2C*']
 
 def get_alt_function(mcu, pin, function):
     '''return alternative function number for a pin'''