packagegroup-ni-xfce: Fix missing packages on x64
packagegroup-ni-xfce: Fix missing packages on x64

RDEPENDS_${PN}_x64 was overriding the RDEPENDS_${PN}, so some packages
were lost. Change to RDEPENDS_${PN}_append_x64.

Natinst-ReviewBoard-ID:146325
Signed-off-by: Heghedus Razvan <0a60b1373e874cee2eab52b3c98f4647a58e91af@ni.com>

ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt