ANDROID: binder: unexport "binder_loaded"

In commit a54f6a76 ("ANDROID: binder: allow changing binder.impl
during boot"), "binder_loaded" was exported, but it is never used
anywhere else, and does not live in any device symbol tables.  So mark
it static and remove the unneeded export.

Bug: 442512016
Cc: Alice Ryhl <aliceryhl@google.com>
Fixes: a54f6a76 ("ANDROID: binder: allow changing binder.impl during boot")
Change-Id: I7468977049c731a3dc37fad1309089df5064ae0b
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>