By default this change only enables amdgpu to address Southern Island boards, but radeon is still the preferred module as amdgpu.c contains the following code (Linux 4.15.2):
amdgpu_drv.c-#ifdef CONFIG_DRM_AMDGPU_SI
amdgpu_drv.c-
amdgpu_drv.c-#if defined(CONFIG_DRM_RADEON) || defined(CONFIG_DRM_RADEON_MODULE)
amdgpu_drv.c:int amdgpu_si_support = 0;
amdgpu_drv.c-MODULE_PARM_DESC(si_support, "SI support (1 = enabled, 0 = disabled (default))");
amdgpu_drv.c-#else
amdgpu_drv.c:int amdgpu_si_support = 1;
amdgpu_drv.c-MODULE_PARM_DESC(si_support, "SI support (1 = enabled (default), 0 = disabled)");
amdgpu_drv.c-#endif

So this commit should not change anything unless radeon_si_support is disabled and amdgpu.si_support is enabled on the kernel CLI:
grubby --args="radeon.si_support=0 radeon.cik_support=0 amdgpu.si_support=1 amdgpu.cik_support=1" --update-kernel DEFAULT

Tested on a R7 250:
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Cape Verde PRO [Radeon HD 7750/8740 / R7 250E] (prog-if 00 [VGA controller])
Subsystem: PC Partner Limited / Sapphire Technology Device a001
Physical Slot: 2
Flags: bus master, fast devsel, latency 0, IRQ 25
Memory at e0000000 (64-bit, prefetchable) [size=256M]
Memory at f0100000 (64-bit, non-prefetchable) [size=256K]
I/O ports at 3100 [size=256]
[virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
Capabilities: [48] Vendor Specific Information: Len=08 <?>
Capabilities: [50] Power Management version 3
Capabilities: [58] Express Legacy Endpoint, MSI 00
Capabilities: [a0] MSI: Enable+ Count=1/1 Maskable- 64bit+
Capabilities: [100] Vendor Specific Information: ID=0001 Rev=1 Len=010 <?>
Capabilities: [150] Advanced Error Reporting
Capabilities: [200] #15
Capabilities: [270] #19
Kernel driver in use: amdgpu
Kernel modules: radeon, amdgpu

This is necessary to get Vulkan working with radv:
$ vulkaninfo
(...)
Presentable Surfaces:
=====================
GPU id : 0 (AMD RADV CAPE VERDE)
Surface type : VK_KHR_xcb_surface
Formats: count = 2
B8G8R8A8_SRGB
B8G8R8A8_UNORM
Present Modes: count = 3
IMMEDIATE_KHR
MAILBOX_KHR
FIFO_KHR

I merged this outside the Pagure UI and it doesn't know to close PRs as merged automatically