agxv: correctly set PBE mipmap info for image views

Previously that would cause issues when trying to interact with any other mipmap level than the first one.

Also set sRGB flag on PBE info when the format is sRGB.

This was found with "dEQP-VK.texture.swizzle.texture_coordinate.r8g8b8a8_unorm_2d_pot_yx" failure.