drivers: target: Move prototype declaration of function to header file target_core_pr.h
Move prototype declaration of function
spc_parse_naa_6h_vendor_specific() from target_core_xcopy.c to header
file target_core_pr.h because it is used by more than one file.
This eliminates the following warning in target_core_spc.c:
drivers/target/target_core_spc.c:138:6: warning: no previous prototype for ‘spc_parse_naa_6h_vendor_specific’ [-Wmissing-prototypes]