Rework platform memory limits

Rework platform memory limits

Some OpenGL tests in openglcts and kc_cts used Vulkan platform class to
get the available system / device memory. The memory limits are not
Vulkan related.

This CL moves the getMemoryLimits function to the base class of all
platforms, so the functions can be accessed from openglcts without
referencing any Vulkan files.

Affects:

dEQP-VK.info.memory_limits
dEQP-VK.api.buffer.suballocation.*
dEQP-VK.api.buffer.dedicated_alloc.*
dEQP-VK.api.object_management.*
dEQP-VK.memory.allocation.*
dEQP-VK.memory.device_group_allocation.*
dEQP-VK.pipeline.render_to_image.*.small.*
dEQP-VK.pipeline.render_to_image.*.huge.*

KHR-GL4*.shader_image_load_store.advanced-*

Components:
Vulkan, OpenGL, Framework

VK-GL-CTS issue: 3360

Change-Id: I0743a83148c946d962fd793c8771f2c3c2e33ecc