llcc: Add declaration of APIs when CONFIG_QCOM_LLCC is not enabled

This change declares set of APIs to fix linking errors seen with client
driver compilation when CONFIG_QCOM_LLCC is not enabled.

llcc manager's client driver doesn't use core llcc driver APIs. Hence
it doesn't need to include llcc-qcom.h. This results into below warning
while compiling client driver.

warning: declaration of 'struct llcc_slice_config' will not be
visible outside of this function [-Wvisibility]

Hence include llcc-qcom.h within llcc-slice.h file. So llcc manager's
client driver doesn't need to directly include llcc-qcom.h file as it
doesn't use any of core driver APIs.

Change-Id: If7232818856876be170af9d2fa7633ff3791d3f2
Signed-off-by: Mayank Rana <mrana@codeaurora.org>