Convert CONFIG_CMD_IMMAP to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_IMMAP

Also move this command out of the cmd/ directory since it is
PowerPC-specific.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/powerpc/lib/Kconfig b/arch/powerpc/lib/Kconfig
new file mode 100644
index 0000000..987cec9
--- /dev/null
+++ b/arch/powerpc/lib/Kconfig
@@ -0,0 +1,8 @@
+config CMD_IMMAP
+	bool "Enable various commands to dump IMMR information"
+	help
+	  This enables various commands such as:
+
+	    siuinfo - print System Interface Unit (SIU) registers
+	    memcinfo - print Memory Controller registers
+	    sitinfo - print System Integration Timers (SIT) registers