machine/stm32: add STM32U585 target definition and runtime

Add processor target (cortex-m33), linker script (2048K flash, 768K RAM),
and arduino-uno-q board target. Runtime initializes 160MHz clock via PLL1
from HSI16, with PWR Range 1 and EPOD booster.

Also add psctype abstraction for timer PSC register width, needed because
the U5 SVD defines PSC as a 16-bit register.

src/machine/machine_stm32f7.go

@@ -712,6 +712,7 @@ func (t *TIM) enableMainOutput() {
 }
 
 type arrtype = uint32
+type psctype = uint32
 type arrRegType = volatile.Register32
 
 const (