Pin numbers for Rock 4C Plus not available
I am using the library on a Rock 4C Plus. I am trying to use GPIO 73 and 74 (pin 31 and 29) 

Blinka version = '8.15.2'
Python version = 3.8.10
OS = Ubuntu 20.04 arm64

```
>>> board.board_id
'ROCK_PI_4C+'
```

Pin assignment:
```
outPin = board.B1
AttributeError: module 'board' has no attribute 'B1'
```

As I understand the mapping is available here:
https://github.com/adafruit/Adafruit_Blinka/blob/main/src/adafruit_blinka/microcontroller/rockchip/rk3399/pin.py#L24-L25

My assumption is that I need to use pin board.B1 and board.B2, but they don't show up. All available pins are shown below:

```
board.ADC_IN0   board.D27       board.D8        board.SDA7
board.CS        board.D28       board.I2C(      board.SPI(
board.D10       board.D29       board.MISO      board.UART2_RX
board.D11       board.D3        board.MOSI      board.UART2_TX
board.D12       board.D31       board.PWM0      board.UART4_RX
board.D13       board.D32       board.SCK       board.UART4_TX
board.D15       board.D33       board.SCL       board.UART_RX
board.D16       board.D35       board.SCL2      board.UART_TX
board.D18       board.D36       board.SCL6      board.ap_board
board.D19       board.D37       board.SCL7      board.board_id
board.D21       board.D38       board.SCLK      board.detector
board.D22       board.D40       board.SDA       board.pin
board.D23       board.D5        board.SDA2      board.sys
board.D24       board.D7        board.SDA6

board.pin
<module 'adafruit_blinka.microcontroller.rockchip.rk3399_t.pin' from '/home/rock/.local/lib/python3.8/site-packages/adafruit_blinka/microcontroller/rockchip/rk3399_t/pin.py'
```


@wgroeneveld Tagging you if you don't mind. Do you happen to know what the problem is?
diff --git a/src/adafruit_blinka/board/radxa/rockpi4.py b/src/adafruit_blinka/board/radxa/rockpi4.py
index 9fdccbc..c8070ed 100644
--- a/src/adafruit_blinka/board/radxa/rockpi4.py
+++ b/src/adafruit_blinka/board/radxa/rockpi4.py
@@ -46,9 +46,9 @@ SCL7 = D5
 SDA = SDA2
 SCL = SCL2
 
-SCLK = D19
-MOSI = D21
-MISO = D23
+SCLK = D23
+MOSI = D19
+MISO = D21
 CS = D24
 SCK = SCLK
 
['src/adafruit_blinka/board/radxa/rockpi4.py']