Convert CONFIG_MONITOR_IS_IN_RAM to Kconfig

This converts the following to Kconfig:
   CONFIG_MONITOR_IS_IN_RAM

As part of this, reword some of the documentation slightly to reflect
that this is in Kconfig and not a define now.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/3c120_defconfig b/configs/3c120_defconfig
index 8c421f0..46dfaf8 100644
--- a/configs/3c120_defconfig
+++ b/configs/3c120_defconfig
@@ -1,5 +1,6 @@
 CONFIG_NIOS2=y
 CONFIG_SYS_CONFIG_NAME="3c120_devboard"
+CONFIG_MONITOR_IS_IN_RAM=y
 CONFIG_SYS_MALLOC_LEN=0x20000
 CONFIG_SYS_MALLOC_F_LEN=0x400
 CONFIG_NR_DRAM_BANKS=1