signal/frv: Move the frv specific si_codes to asm-generic/siginfo.h

Having si_codes in many different files simply encourages duplicate definitions
that can cause problems later.  To avoid that merce the frv specific si_codes
into uapi/asm-generic/siginfo.h

This allows the removal of arch/frv/uapi/include/asm/siginfo.h as the last
last meaningful definition it held was FPE_MDAOVF.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>