KeyStone RIO: use up to RIO_MAX_MSG_SIZE for message size on KeyStone devices

Previously it was limited to 1552. It allows now to use messages of 4096 bytes.

Signed-off-by: Aurelien Jacquiot <a-jacquiot@ti.com>
RIO: add capability to change MTU with ifconfig in RIONET

 By default the MTU is set to the maximum RapidIO message size
 minus 14 bytes of Ethernet header (and eventually alignment padding)
 but we may need to change this MTU to either the standard
 Ethernet MTU (1500) or to a custom one.

Signed-off-by: Aurelien Jacquiot <a-jacquiot@ti.com>
Fix C6x ptrace to call generic ptrace request handling

 This is needed for ptrace requests like PTRACE_SETOPTIONS,
 PTRCE_GETSIGINFO, etc that are not handled by C6x specific
 ptrace management.

Signed-off-by: Aurelien Jacquiot <a-jacquiot@ti.com>