pfla02: Fix RAM detection and support 1 bank SOM

In case of 2 banks, the address space of the first CS must be defined
and not let to the higher value.

Add support for SOM with a single bank of RAM. It was tested with i.MX6Q
modules in the following configurations:

- 2 Banks, 4 GB
- 2 Banks, 1 GB
- 1 Bank,  1 GB

Signed-off-by: Stefano Babic <sbabic@denx.de>
diff --git a/board/phytec/pfla02/Kconfig b/board/phytec/pfla02/Kconfig
index 142a122..f4da68b 100644
--- a/board/phytec/pfla02/Kconfig
+++ b/board/phytec/pfla02/Kconfig
@@ -9,4 +9,10 @@
 config SYS_CONFIG_NAME
 	default "pfla02"
 
+config SPL_DRAM_1_BANK
+	bool "DRAM on just one bank"
+	help
+	  activate, if the module has just one bank
+	  of RAM
+
 endif