ia64: Use Linux kABI for syscall return

It changes the ia64 INTERNAL_SYSCALL_NCS macro to return a negative
value instead of the 'r10' register value on the 'err' macro argument.

The macro INTERNAL_SYSCALL_DECL is no longer required, and the
INTERNAL_SYSCALL_ERROR_P macro follows the other Linux kABIs.

Checked on ia64-linux-gnu.