sparc: Use Linux kABI for syscall return

It changes the sparc internal_syscall* macros to return a negative
value instead of the 'g1' register value in the 'err' macro argument.
The __SYSCALL_STRING macro is also changed to no set the 'g1'
value, since 'o1' already holds all the required information
to check if syscall has failed.

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

Checked on sparc64-linux-gnu and sparcv9-linux-gnu. It fixes
the sporadic issues on sparc32 where clock_nanosleep does not
act as cancellation entrypoint.