atsam: Use enumerations for buses and reserve pins

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

config/generic-duet2.cfg

@@ -94,7 +94,7 @@ position_max: 250
 
 [tmc2660 stepper_x]
 cs_pin: PD14 # X_SPI_EN Required for communication
-spi_bus: 1 # All TMC2660 drivers are connected to USART1, which is bus 1 on the sam4e port
+spi_bus: usart1 # All TMC2660 drivers are connected to USART1
 microsteps: 16
 interpolate: True # 1/16 micro-steps interpolated to 1/256
 run_current: 1.000
@@ -112,7 +112,7 @@ position_max: 210
 
 [tmc2660 stepper_y]
 cs_pin: PC9
-spi_bus: 1
+spi_bus: usart1
 microsteps: 16
 interpolate: True
 run_current: 1.000
@@ -130,7 +130,7 @@ position_max: 200
 
 [tmc2660 stepper_z]
 cs_pin: PC10
-spi_bus: 1
+spi_bus: usart1
 microsteps: 16
 interpolate: True
 run_current: 1.000
@@ -145,7 +145,7 @@ step_distance: .0025
 
 [tmc2660 stepper_z1]
 cs_pin: PD25
-spi_bus: 1
+spi_bus: usart1
 microsteps: 16
 interpolate: True
 run_current: 1.000
@@ -160,7 +160,7 @@ step_distance: .0025
 
 [tmc2660 stepper_z2]
 cs_pin: PD26
-spi_bus: 1
+spi_bus: usart1
 microsteps: 16
 interpolate: True
 run_current: 1.000
@@ -175,7 +175,7 @@ step_distance: .0025
 
 [tmc2660 stepper_z3]
 cs_pin: PC28
-spi_bus: 1
+spi_bus: usart1
 microsteps: 16
 interpolate: True
 run_current: 1.000
@@ -201,7 +201,7 @@ max_temp: 250
 
 [tmc2660 extruder0]
 cs_pin: PC17
-spi_bus: 1
+spi_bus: usart1
 microsteps: 16
 interpolate: True
 run_current: 1.000
@@ -227,7 +227,7 @@ max_temp: 250
 
 [tmc2660 extruder1]
 cs_pin: PC25
-spi_bus: 1
+spi_bus: usart1
 microsteps: 16
 interpolate: True
 run_current: 1.000
@@ -253,7 +253,7 @@ max_temp: 250
 
 [tmc2660 extruder2]
 cs_pin: PD23
-spi_bus: 1
+spi_bus: usart1
 microsteps: 16
 interpolate: True
 run_current: 1.000
@@ -279,7 +279,7 @@ max_temp: 250
 
 [tmc2660 extruder3]
 cs_pin: PD24
-spi_bus: 1
+spi_bus: usart1
 microsteps: 16
 interpolate: True
 run_current: 1.000