The warm reset function was still using the obsolete API.
Replace it by the new one and move the file to the proper c file.

Change the function names to stick to the file convention as
suggested by Paul Walmsley <paul@pwsan.com>:
prm_xxx -> prminst_xxx
Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>