Bug #9: Both TX and RX SPI init params had platform_ops = NULL, causing
adf4382_init() -> no_os_spi_init() to fail with -EINVAL. Fixed by setting
platform_ops = &stm32_spi_ops and passing stm32_spi_extra with correct CS
port/pin for each device.
Bug #10: stm32_spi_write_and_read() never toggled chip select. Since TX
and RX ADF4382A share SPI4, every register write hit both PLLs. Rewrote
stm32_spi.c to assert CS LOW before transfer and deassert HIGH after,
using stm32_spi_extra metadata. Backward-compatible: legacy callers
(e.g., AD9523) with cs_port=NULL skip CS management.
Also widened chip_select from uint8_t to uint16_t in no_os_spi.h since
STM32 GPIO_PIN_xx values (e.g., GPIO_PIN_14=0x4000) overflow uint8_t.
10/10 tests pass (8 original + 2 new regression tests).
Jason