defconfig: Modify busPM as a loadable ko in perf deconfig

busPM is used for bus profiling of various usecases. The busPM feature is
a loadable kernel module and was accidentally marked as linked feature for
the perf deconfig. Make the change to mark busPM as a loadable kernel
module.

Change-Id: I5b2e2176d94f2a5c1a4a862a16de6b30d25f53b0
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>