Historically, pt_regs have had orig_r8, an overloaded container for
(1) backup copy of r8 (syscall number Trap Exceptions)
(2) additional system state: (syscall/Exception/Interrupt)
There is no point in keeping (1) since syscall number is never clobbered
in-place, in pt_regs, unlike r0 which duals as first syscall arg as well
as syscall return value and in case of syscall restart, the orig arg0
needs restoring (from orig_r0) after having been updated in-place with
syscall ret value.
This further paves way to convert (2) to contain ECR itself (rather than
current madeup values)
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>