freedreno/a6xx: a750 support

• Some random fixes I found along the way
• Convert driver-params enums -> structs, since the enums were getting unwieldy and structs let us re-use the driver-params population between the old push-consts path and the new driver-ubo path
• Track # of app/api UBOs vs total # of UBOs (including driver UBOs).. the gallium driver needs this to overwrite driver UBO slots with unused API level const buffers that are bound
• Add support for the driver-UBO path (load_shader_consts_via_preamble) so that a750 works properly

TODO

• Can we switch all a7xx over to the new path and drop load_shader_consts_via_preamble? This would let us drop all the runtime if/else and just rely on compile-time if (CHIP >= A7XX)...

Note, I don't actually have any a750, this was tested on x1-85 with the HACK patch to enable load_shader_consts_via_preamble