drm/amd/display: fix non-x86/PPC64 compilation

Need to protect FP DMCUB code with CONFIG_DRM_AMD_DC_DCN.
Fixes build failures like the following on arm64:
ERROR: modpost: "__floatunsidf" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
ERROR: modpost: "__divdf3" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
ERROR: modpost: "fma" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
ERROR: modpost: "__adddf3" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
ERROR: modpost: "__fixdfsi" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
ERROR: modpost: "__muldf3" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
ERROR: modpost: "__floatsidf" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
ERROR: modpost: "__fixunsdfsi" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!

Fixes: 85f4bc0c ("drm/amd/display: Add SubVP required code")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c

@@ -370,6 +370,7 @@ void dc_dmub_srv_query_caps_cmd(struct dmub_srv *dmub)
 	}
 }
 
+#ifdef CONFIG_DRM_AMD_DC_DCN
 /**
  * ***********************************************************************************************
  * populate_subvp_cmd_drr_info: Helper to populate DRR pipe info for the DMCUB subvp command
@@ -698,6 +699,7 @@ void dc_dmub_setup_subvp_dmub_command(struct dc *dc,
 	dc_dmub_srv_cmd_execute(dc->ctx->dmub_srv);
 	dc_dmub_srv_wait_idle(dc->ctx->dmub_srv);
 }
+#endif
 
 bool dc_dmub_srv_get_diagnostic_data(struct dc_dmub_srv *dc_dmub_srv, struct dmub_diagnostic_data *diag_data)
 {

drivers/gpu/drm/amd/display/dc/dcn32/Makefile

@@ -27,7 +27,6 @@ ifdef CONFIG_CC_IS_GCC
 ifeq ($(call cc-ifversion, -lt, 0701, y), y)
 IS_OLD_GCC = 1
 endif
-dcn32_ccflags += -mhard-float
 endif
 
 ifdef CONFIG_X86