[qsd8250]: Add usb charging support in LK bootloader.

Add usb battery charging support for qsd8250_surf and qsd8250_ffa
targets in lk bootloader. USB charging is enabled only when
device goes into fastboot mode.
diff --git a/target/init.c b/target/init.c
index e6f114c..933ef19 100644
--- a/target/init.c
+++ b/target/init.c
@@ -55,3 +55,8 @@
 __WEAK void reboot_device(unsigned reboot_reason)
 {
 }
+
+__WEAK void target_battery_charging_enable
+                 (unsigned enable, unsigned disconnect)
+{
+}