x86: dfi-bt700: Fix up adjustment of CONFIG_TEXT_BASE

With recent CONFIG_TEXT_BASE changes, there are inconsistencies between
several settings.

Adjust CONFIG_SYS_MONITOR_LEN to allow more code space. Move the MRC
cache out of the way too.

Fixes: 5d1c8342 ("x86: dfi-bt700: Adjust CONFIG_TEXT_BASE")
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>