nrf52: enable and fix build for SPI BITORDER

arch/arm/Kconfig

@@ -211,6 +211,7 @@ config ARCH_CHIP_NRF52
 	select ARCH_HAVE_TICKLESS
 	#select ARCH_HAVE_MPU
 	#select ARM_HAVE_MPU_UNIFIED
+	select ARCH_HAVE_SPI_BITORDER
 	select ARCH_HAVE_FPU
 	select ARCH_HAVE_PWM_MULTICHAN
 	select ARCH_HAVE_SERIAL_TERMIOS

arch/arm/src/nrf52/nrf52_spi.c

@@ -920,6 +920,7 @@ static int nrf52_spi_hwfeatures(FAR struct spi_dev_s *dev,
   FAR struct nrf52_spidev_s *priv = (FAR struct nrf52_spidev_s *)dev;
   uint32_t setbits = 0;
   uint32_t clrbits = 0;
+  uint32_t regval;
 
   spiinfo("features=%08x\n", features);