I've also added the line, kld_list="/boot/modules/radeonkms.ko" in to /etc/rc.conf file.
According to this X.org wikivgapci0@pci0:0:1:0: class=0x030000 card=0x078e1028 chip=0x98e41002 rev=0xd2 hdr=0x00
vendor = 'Advanced Micro Devices, Inc. [AMD/ATI]'
device = 'Stoney [Radeon R2/R3/R4/R5 Graphics]'
class = display
the GPU with the engineering name STONEY is from the Volcanic Islands video card family. The AMD-GPU-Matrix comments the use of the "amdgpu" kernel module (third row, counting from last row up).
Try
kld_list="amdgpu"
in /etc/rc.conf.