bootstage: Fix dependency for BOOTSTAGE_RECORD_COUNT

At present these three Kconfigs exist even when bootstage is not enabled.
This is not necessary since bootstage.c is only built if BOOTSTAGE is
enabled.

Make them conditional. Also fix up the overflow message to mention TPL.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/Kconfig.boot b/common/Kconfig.boot
index 70c02b9..e650c60 100644
--- a/common/Kconfig.boot
+++ b/common/Kconfig.boot
@@ -449,6 +449,7 @@
 
 config BOOTSTAGE_RECORD_COUNT
 	int "Number of boot stage records to store"
+	depends on BOOTSTAGE
 	default 30
 	help
 	  This is the size of the bootstage record list and is the maximum
@@ -456,6 +457,7 @@
 
 config SPL_BOOTSTAGE_RECORD_COUNT
 	int "Number of boot stage records to store for SPL"
+	depends on SPL_BOOTSTAGE
 	default 5
 	help
 	  This is the size of the bootstage record list and is the maximum
@@ -463,6 +465,7 @@
 
 config TPL_BOOTSTAGE_RECORD_COUNT
 	int "Number of boot stage records to store for TPL"
+	depends on TPL_BOOTSTAGE
 	default 5
 	help
 	  This is the size of the bootstage record list and is the maximum