Nokia RX-51: Move comment about CONFIG_SYS_TEXT_BASE to correct place

In commit commit 278b90ce ("configs: Migrate CONFIG_SYS_TEXT_BASE") was
moved definition for CONFIG_SYS_TEXT_BASE option but author probably forgot
to move also comment for lines which are moving. So do it now!

Signed-off-by: Pali Rohár <pali@kernel.org>