machine/stm32: add STM32U5 SPI support

Add SPIv2 driver for STM32U5 using TXDR/RXDR and CFG1/CFG2 registers,
which differ from the classic SPI peripheral on older STM32 families.
Implements Configure() and single-byte Transfer().

Add SPI1 peripheral and pin definitions to arduino-uno-q board.
Exclude stm32u5 from the shared classic SPI build tag.

src/machine/machine_stm32_spi.go

@@ -1,4 +1,4 @@
-//go:build stm32 && !stm32f7x2 && !stm32l5x2 && !stm32g0
+//go:build stm32 && !stm32f7x2 && !stm32l5x2 && !stm32g0 && !stm32u5
 
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