Adapt to new Linux syscall ABI
Adapt to new Linux syscall ABI

The Linux syscall ABI has finally settled in OpenRISC Linux 2.6.38.  This
new ABI is, externally, the same as the regular C function call ABI with
a couple of exceptions:

i)  r9 does not need to be set as the link register is not used for
    returning from the user interrupt; r9 is still preserved across call

ii) r11 is used when entering the user interrupt to determine which
    syscall to execute; r11 will contain function's return value upon
    return (i.e. the syscall result)

Aside from those exceptions, a syscall should behave like a regular function
call with all that implies with respect to call-saved and call-clobbered
registers.

For completeness, the register characteristics are:

call clobbered: r3-r8, r11-r13, and odd numbered regs from r15-r31
call saved:     r1,r2,r9,r10, and even numbered regs from r14-r30

skristiansson/uClibc-or1k,skristiansson/uClibc-or1k,skristiansson/uClibc-or1k,skristiansson/uClibc-or1k