powerpc: syscall support up to 6 arguments
powerpc: syscall support up to 6 arguments

As reported by Kristof Provost.

Signed-off-by: Bernhard Reutner-Fischer <ce1ac9e9ad16abccd7821f371ad381197b4768ac@gmail.com>

hjl-tools/uClibc,brgl/uclibc-ng,hjl-tools/uClibc,brgl/uclibc-ng,kraj/uclibc-ng,brgl/uclibc-ng,foss-for-synopsys-dwc-arc-processors/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,hjl-tools/uClibc,wbx-github/uclibc-ng,brgl/uclibc-ng,hjl-tools/uClibc,ffainelli/uClibc,majek/uclibc-vx32,kraj/uClibc,wbx-github/uclibc-ng,groundwater/uClibc,hjl-tools/uClibc,kraj/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,kraj/uclibc-ng,majek/uclibc-vx32,groundwater/uClibc,ffainelli/uClibc,groundwater/uClibc,wbx-github/uclibc-ng,ffainelli/uClibc,wbx-github/uclibc-ng,kraj/uClibc,kraj/uclibc-ng,foss-for-synopsys-dwc-arc-processors/uClibc,kraj/uclibc-ng,majek/uclibc-vx32,ffainelli/uClibc,majek/uclibc-vx32,ffainelli/uClibc,kraj/uClibc,groundwater/uClibc,groundwater/uClibc