Fastboot: Use AServiceManager_waitForService instead of AServiceManager_getService

AServiceManager_getService waits unncessarily waits for 5 seconds if
service is not available. Use isDeclared() and waitForService() instead.

Bug: 261759425
Test: build and flash
Change-Id: I20a5f422ca0c26c6e9e183e6636b30a2f19e76d3
Signed-off-by: Sandeep Dhavale <dhavale@google.com>