drm/amdgpu: fix set scaling mode Full/Full aspect/Center not works on vga and dvi connectors

stable inclusion
form stable-v5.10.82
commit 04c586a601dc0acb8e739205db350ab660dffc4f
bugzilla: 185877 https://gitee.com/openeuler/kernel/issues/I4QU6V

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=04c586a601dc0acb8e739205db350ab660dffc4f



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commit bf552083 upstream.

amdgpu_connector_vga_get_modes missed function amdgpu_get_native_mode
which assign amdgpu_encoder->native_mode with *preferred_mode result in
amdgpu_encoder->native_mode.clock always be 0. That will cause
amdgpu_connector_set_property returned early on:
if ((rmx_type != DRM_MODE_SCALE_NONE) &&
	(amdgpu_encoder->native_mode.clock == 0))
when we try to set scaling mode Full/Full aspect/Center.
Add the missing function to amdgpu_connector_vga_get_mode can fix this.
It also works on dvi connectors because
amdgpu_connector_dvi_helper_funcs.get_mode use the same method.

Signed-off-by: hongao <hongao@uniontech.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>