memory: brcmstb_dpfe: Allow building Broadcom STB DPFE as module

Allow building the Broadcom STB DPFE driver as a module, it is already a
platform driver proper with all of the resource releasing device
managed.
Signed-off-by: NFlorian Fainelli <f.fainelli@gmail.com>
Acked-by: NMarkus Mayer <mmayer@broadcom.com>
Link: https://lore.kernel.org/r/20210924031459.8911-1-f.fainelli@gmail.comSigned-off-by: NKrzysztof Kozlowski <krzysztof.kozlowski@canonical.com>

drivers/memory/Kconfig

@@ -55,8 +55,8 @@ config ATMEL_EBI
 	  SRAMs, ATA devices, etc.
 
 config BRCMSTB_DPFE
-	bool "Broadcom STB DPFE driver" if COMPILE_TEST
-	default y if ARCH_BRCMSTB
+	tristate "Broadcom STB DPFE driver"
+	default ARCH_BRCMSTB
 	depends on ARCH_BRCMSTB || COMPILE_TEST
 	help
 	  This driver provides access to the DPFE interface of Broadcom