fastbootd: Implement the getvar command.

This implements basic "fastboot getvar" support, including commands supported
by IBootControl.

Bug: 78793464
Test: fastboot getvar <fastboot variable>

Change-Id: Iee1a7b3f43dea46f80dcdf73c45034e2ffe4727d
diff --git a/fastboot/Android.bp b/fastboot/Android.bp
index 51cc62a..aa88a8a 100644
--- a/fastboot/Android.bp
+++ b/fastboot/Android.bp
@@ -96,6 +96,8 @@
         "device/fastboot_device.cpp",
         "device/main.cpp",
         "device/usb_client.cpp",
+        "device/utility.cpp",
+        "device/variables.cpp",
     ],
 
     shared_libs: [
@@ -103,6 +105,7 @@
         "libext4_utils",
         "libsparse",
         "liblog",
+        "android.hardware.boot@1.0",
         "libbootloader_message",
         "libhidltransport",
         "libhidlbase",