picosam9g45: adopt CONFIG_SYS_PROMPT

Commit 181bd9dc introduced Kconfig selection
for SYS_PROMPT. When applying the new picosam9g45 board this change slipped
through, adopt it.
Signed-off-by: NAndreas Bießmann <andreas.devel@googlemail.com>

configs/picosam9g45_defconfig

@@ -3,6 +3,7 @@ CONFIG_ARCH_AT91=y
 CONFIG_TARGET_PICOSAM9G45=y
 CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="AT91SAM9M10G45,SYS_USE_MMC"
+CONFIG_SYS_PROMPT="U-Boot> "
 # CONFIG_CMD_BDI is not set
 # CONFIG_CMD_IMI is not set
 # CONFIG_CMD_IMLS is not set

include/configs/picosam9g45.h

@@ -156,7 +156,6 @@
 
 #define CONFIG_BAUDRATE			115200
 
-#define CONFIG_SYS_PROMPT	"U-Boot> "
 #define CONFIG_SYS_CBSIZE	256
 #define CONFIG_SYS_MAXARGS	16
 #define CONFIG_SYS_PBSIZE	(CONFIG_SYS_CBSIZE  \