tests/driver_nvram_spi: simplified Makefile

tests/driver_nvram_spi/Makefile

@@ -6,29 +6,16 @@ FEATURES_REQUIRED = periph_spi periph_gpio
 USEMODULE += nvram_spi
 USEMODULE += xtimer
 
-ifneq (,$(TEST_NVRAM_SPI_DEV))
-  CFLAGS += -DTEST_NVRAM_SPI_DEV=$(TEST_NVRAM_SPI_DEV)
-else
-  # set arbitrary default
-  CFLAGS += -DTEST_NVRAM_SPI_DEV=SPI_0
-endif
-ifneq (,$(TEST_NVRAM_SPI_CS))
-  CFLAGS += -DTEST_NVRAM_SPI_CS=$(TEST_NVRAM_SPI_CS)
-else
-  # set arbitrary default
-  CFLAGS += -DTEST_NVRAM_SPI_CS=GPIO_PIN\(0,0\)
-endif
-ifneq (,$(TEST_NVRAM_SPI_SIZE))
-  CFLAGS += -DTEST_NVRAM_SPI_SIZE=$(TEST_NVRAM_SPI_SIZE)
-else
-  # set tiny arbitrary default
-  CFLAGS += -DTEST_NVRAM_SPI_SIZE=64
-endif
-ifneq (,$(TEST_NVRAM_SPI_ADDRESS_COUNT))
-  CFLAGS += -DTEST_NVRAM_SPI_ADDRESS_COUNT=$(TEST_NVRAM_SPI_ADDRESS_COUNT)
-else
-  # set 1 address byte by default, increase if using a larger module for test.
-  CFLAGS += -DTEST_NVRAM_SPI_ADDRESS_COUNT=1
-endif
+# set default device parameters in case they are undefined
+TEST_NVRAM_SPI_DEV           ?= SPI_0
+TEST_NVRAM_SPI_CS            ?= GPIO_PIN\(0,0\)
+TEST_NVRAM_SPI_SIZE          ?= 64
+TEST_NVRAM_SPI_ADDRESS_COUNT ?= 1
+
+# export parameters
+CFLAGS += -DTEST_NVRAM_SPI_DEV=$(TEST_NVRAM_SPI_DEV)
+CFLAGS += -DTEST_NVRAM_SPI_CS=$(TEST_NVRAM_SPI_CS)
+CFLAGS += -DTEST_NVRAM_SPI_SIZE=$(TEST_NVRAM_SPI_SIZE)
+CFLAGS += -DTEST_NVRAM_SPI_ADDRESS_COUNT=$(TEST_NVRAM_SPI_ADDRESS_COUNT)
 
 include $(RIOTBASE)/Makefile.include