dev_freq: devfreq_spdm: make cci_clk optional indicator

Enable dev_freq SPDM support in order to increase BIMC
vote based on bus rejection rate. Make cci_clk an optional
property as it's not always a relevant indicator of cpu performance.

CRs-Fixed: 1025515
Change-Id: I713cc396c8d563735981547e0dc18a63f6f15180
Signed-off-by: David Dai <daidavid1@codeaurora.org>