keyboard_scan: Add option to not handle special key combinations

On some boards, the special alt-volup-r/h combinations do not make
a lot of sense, so we can just not process them and save a little
bit of code space.

BRANCH=none
BUG=b:37422577
TEST=Flash hammer, alt-volup-r/h does not do anything special
TEST=make newsizes shows we save 124 bytes in hammer RW.

Change-Id: I92770fd6b8ff90780162a6b1de428a550bb44e9b
Reviewed-on: https://chromium-review.googlesource.com/495967
Commit-Ready: Nicolas Boichat <drinkcat@chromium.org>
Tested-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>

common/keyboard_scan.c

@@ -272,6 +272,7 @@ static int read_matrix(uint8_t *state)
 	return pressed ? 1 : 0;
 }
 
+#ifdef CONFIG_KEYBOARD_RUNTIME_KEYS
 /**
  * Check special runtime key combinations.
  *
@@ -365,6 +366,7 @@ static int check_runtime_keys(const uint8_t *state)
 
 	return 0;
 }
+#endif /* CONFIG_KEYBOARD_RUNTIME_KEYS */
 
 /**
  * Check for ghosting in the keyboard state.
@@ -506,9 +508,11 @@ static int check_keys_changed(uint8_t *state)
 		CPRINTF("]\n");
 #endif
 
+#ifdef CONFIG_KEYBOARD_RUNTIME_KEYS
 		/* Swallow special keys */
 		if (check_runtime_keys(state))
 			return 0;
+#endif
 
 #ifdef CONFIG_KEYBOARD_PROTOCOL_MKBP
 		keyboard_fifo_add(state);

include/config.h

@@ -1515,6 +1515,12 @@
 /*  Print keyboard scan time intervals. */
 #undef CONFIG_KEYBOARD_PRINT_SCAN_TIMES
 
+/*
+ * Support for extra runtime key combinations (e.g. alt+volup+h/r for hibernate
+ * and warm reboot, respectively).
+ */
+#define CONFIG_KEYBOARD_RUNTIME_KEYS
+
 /*
  * Call board-supplied keyboard_suppress_noise() function when the debounced
  * keyboard state changes.  Some boards use this to send a signal to the audio