[PGO] Move value profile format related structures and APIs to common file

This is the last step to enable profile runtime to share the same value prof
data format and reader/writer code with llvm host tools. The VP related 
data structures are moved to a section in InstrProfData.inc enabled with macro
INSTR_PROF_VALUE_PROF_DATA, and common API implementations are enabled with
INSTR_PROF_COMMON_API_IMPL. There should be no functional change.

llvm-svn: 254235