qcom: peripheral-loader: Introduce an API to free relocatable memory

Give implementations the freedom to separately invoke
an API that frees relocatable memory, instead of mandatorily
freeing the memory in shutdown().

Change-Id: I802e06fd16c20a777066331ee490f51bcc019b8b
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>