spmi: spmi-pmic-arb-debug: add clock management support

Add support to enable and disable the clock used by the SPMI PMIC
arbiter debug bus.  This is needed to avoid unclocked accesses.

Change-Id: If9eee1317a88c143452d8b46b89aff89d1e956b7
Signed-off-by: David Collins <collinsd@codeaurora.org>