Change vertex buffer format to VK_FORMAT_R8G8B8A8_UNORM

Change vertex buffer format to VK_FORMAT_R8G8B8A8_UNORM

Change the vertex buffer format to VK_FORMAT_R8G8B8A8_UNORM
in spirv1p4.entrypoint* tests to make the tests pass, while
waiting on a fix in Amber.

Affects:
dEQP-VK.spirv_assembly.instruction.spirv1p4.entrypoint*

Components: Vulkan

VK-GL-CTS issue: 1992

Change-Id: Icb97b7328c2e1a61c1e1c20d7dda0449738619e1