fbd-dev-leds: support for multicolor LEDs

Add support for multicolor LEDs as supported by the kernel.
Used by Qualcomm devices such as SHIFT 6mq, OnePlus 6, etc.

Documentation:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/testing/sysfs-class-led-multicolor

Co-Developed-by: Dylan Van Assche <me@dylanvanassche.be>

src/fbd-ledctrl.c

@@ -17,6 +17,7 @@
 #include <unistd.h>
 
 #define LED_BRIGHTNESS_ATTR "brightness"
+#define LED_MULTI_INTENSITY_ATTR "multi_intensity"
 #define LED_PATTERN_ATTR    "pattern"
 #define LED_REPEAT_ATTR     "repeat"
 #define LED_TRIGGER_ATTR    "trigger"
@@ -126,6 +127,9 @@ set_perms (const char *sysfs_path, const char *trigger, const char *gname)
   if (!set_sysfs_attr_perm (sysfs_path, LED_BRIGHTNESS_ATTR, group->gr_gid))
       return FALSE;
 
+  // Attribute is optional
+  set_sysfs_attr_perm (sysfs_path, LED_MULTI_INTENSITY_ATTR, group->gr_gid);
+
   if (!g_strcmp0 (trigger, LED_TRIGGER_PATTERN)) {
     if (!set_sysfs_attr_perm (sysfs_path, LED_PATTERN_ATTR, group->gr_gid))
       success = FALSE;