x86: minnowmax: 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.

Add documentation on how to make this change safely.

Fixes: 66e2c665f3b6 ("x86: minnowmax: Adjust CONFIG_TEXT_BASE")
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/configs/minnowmax_defconfig b/configs/minnowmax_defconfig
index 679b6e3..b93c0d7 100644
--- a/configs/minnowmax_defconfig
+++ b/configs/minnowmax_defconfig
@@ -18,6 +18,7 @@
 CONFIG_GENERATE_MP_TABLE=y
 CONFIG_HAVE_ACPI_RESUME=y
 CONFIG_SEABIOS=y
+CONFIG_SYS_MONITOR_LEN=2097152
 CONFIG_FIT=y
 CONFIG_FIT_SIGNATURE=y
 CONFIG_BOOTSTAGE=y