minui: Allow skipping EV_REL input devices.

This is causing recovery to skip real input devices on some
samsung phones where sensors are registered as input devices.
So there more then 16 of them. (ex. ks01lte)
And EV_REL input devices already disabled in recovery ui.cpp if
BOARD_RECOVERY_NEEDS_REL_INPUT is not set. So do same here not to exceed
the limit of MAX_DEVICES

[javelinanddart]: Move this to an opt-in flag so that we can document
  what devices need this in the device tree, since otherwise we'll
  forget to port this and what devices need this flag. Additionally,
  an opt-in flag makes more sense for select devices needing
  non-standard behavior. The flag is used as follows:
  TARGET_RECOVERY_SKIP_EV_REL_INPUT := true

[aleasto]: Move from a compiletime flag to a runtime prop

Change-Id: If3d6e29d00229278a8ef3dfa445393c9f3d5f361
(cherry picked from commit 331afccf4a9b81ddf22500872b7260b532e15c41)
(cherry picked from commit e7597e934e909112c462024e49a5f43af9bbe341)
diff --git a/minui/events.cpp b/minui/events.cpp
index 17a9d5e..b4beaa9 100644
--- a/minui/events.cpp
+++ b/minui/events.cpp
@@ -32,6 +32,7 @@
 #include <string>
 
 #include <android-base/strings.h>
+#include <android-base/properties.h>
 #include <android-base/unique_fd.h>
 
 #include "minui/minui.h"
@@ -63,6 +64,11 @@
 static size_t g_ev_dev_count = 0;
 static size_t g_ev_misc_count = 0;
 
+static bool should_skip_ev_rel() {
+  static bool prop = android::base::GetBoolProperty("ro.recovery.skip_ev_rel_input", false);
+  return prop;
+}
+
 static bool test_bit(size_t bit, unsigned long* array) { // NOLINT
   return (array[bit / BITS_PER_LONG] & (1UL << (bit % BITS_PER_LONG))) != 0;
 }
@@ -76,9 +82,12 @@
     return false;
   }
 
-  // We assume that only EV_KEY, EV_REL, and EV_SW event types are ever needed. EV_ABS is also
-  // allowed if allow_touch_inputs is set.
-  if (!test_bit(EV_KEY, ev_bits) && !test_bit(EV_REL, ev_bits) && !test_bit(EV_SW, ev_bits)) {
+  // We assume that only EV_ABS, EV_KEY, EV_REL, and EV_SW event types are ever needed.
+  // EV_ABS is only allowed if allow_touch_inputs is set.
+  // EV_REL can be explicitly disallowed. This is needed to skip sensor inputs on some devices.
+  if (!test_bit(EV_KEY, ev_bits) &&
+      !test_bit(EV_SW, ev_bits) &&
+      (should_skip_ev_rel() || !test_bit(EV_REL, ev_bits))) {
     if (!allow_touch_inputs || !test_bit(EV_ABS, ev_bits)) {
       return false;
     }