d3d: don't use the inital values on texture creating

Althought this is an optimization, it won't be used often with the texture pool.
So it's cleaner to remove it, mostly for videocommon.
VideoCommon: don't load texture lvl 0 on creation

There was an optimization which needs this, but now every backends just calls Load() in Create. So this is moved into VideoCommon.
VideoCommon: drop textureCache optimization to reuse entrys

This slows down a lot, but this optimization will also be replaced by the texture pool.
ogl: drop pcfmt

Core profile doesn't support all needed texture formats, so we decode them all on cpu.
This commit also drops the code to load the not-decoded textures.
VideoCommon: create Texture Pool

again...

please see revision 6cece6b486670dd149c827053a84754c98397ccc for more details.

This partially reverts 8923968b47ab27f571ff7464dc34143001c5a567
VideoCommon: mark texpool indexes as const