use new sdbus++ camelcase

Change I17a8d7479556596a3cf252b3f4eae9c8df547189 will change
how sdbus++ generates names which start with an acronym.
Prepare for this by keying off the SDBUSPP_NEW_CAMELCASE
define to use the new format.

Changes:
    vSPString -> vspString

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Idec24c3e2d58abca39fe236051f28567b626e260