remoteproc: qcom: Add SLPI rproc support to load and boot slpi proc.

This patch add slpi remoteproc support in existing adsp rproc driver.

Signed-off-by: Avaneesh Kumar Dwivedi <akdwived@codeaurora.org>
[bjorn: documented aggre2 and px-supply]
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>