ANDROID: CONFIG_MODPROBE_PATH to toolbox's modprobe

Early loading of pKVM modules (i.e. before deprivilege) implies to let
the kernel call modprobe. Notice this doesn't really enable
request_module: UMH is still "disabled" due to
CONFIG_STATIC_USERMODEHELPER_PATH="".

Bug: 278749606
Bug: 254835242
Change-Id: I753ac4177e5017f7d913804bb8439f676d7c2fd8
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
(cherry picked from commit 425c421e)