mesa: Fix MESA_FORMAT names containg SIGNED

mesa: Fix MESA_FORMAT names containg SIGNED

Update comments. Replace format names containing SIGNED with
SNORM appended w/decoration per the format name spec:

    s/MESA_FORMAT_SIGNED_R8\b/MESA_FORMAT_R_SNORM8/g
    s/MESA_FORMAT_SIGNED_RG88_REV\b/MESA_FORMAT_R8G8_SNORM/g
    s/MESA_FORMAT_SIGNED_RGBX8888\b/MESA_FORMAT_X8B8G8R8_SNORM/g
    s/MESA_FORMAT_SIGNED_RGBA8888\b/MESA_FORMAT_A8B8G8R8_SNORM/g
    s/MESA_FORMAT_SIGNED_RGBA8888_REV\b/MESA_FORMAT_R8G8B8A8_SNORM/g
    s/MESA_FORMAT_SIGNED_R16\b/MESA_FORMAT_R_SNORM16/g
    s/MESA_FORMAT_SIGNED_GR1616\b/MESA_FORMAT_R16G16_SNORM/g
    s/MESA_FORMAT_SIGNED_RGB_16\b/MESA_FORMAT_RGB_SNORM16/g
    s/MESA_FORMAT_SIGNED_RGBA_16\b/MESA_FORMAT_RGBA_SNORM16/g
    s/MESA_FORMAT_SIGNED_A8\b/MESA_FORMAT_A_SNORM8/g
    s/MESA_FORMAT_SIGNED_I8\b/MESA_FORMAT_I_SNORM8/g
    s/MESA_FORMAT_SIGNED_L8\b/MESA_FORMAT_L_SNORM8/g
    s/MESA_FORMAT_SIGNED_A16\b/MESA_FORMAT_A_SNORM16/g
    s/MESA_FORMAT_SIGNED_I16\b/MESA_FORMAT_I_SNORM16/g
    s/MESA_FORMAT_SIGNED_L16\b/MESA_FORMAT_L_SNORM16/g
    s/MESA_FORMAT_SIGNED_AL88\b/MESA_FORMAT_L8A8_SNORM/g
    s/MESA_FORMAT_SIGNED_RG88\b/MESA_FORMAT_G8R8_SNORM/g
    s/MESA_FORMAT_SIGNED_RG1616\b/MESA_FORMAT_G16R16_SNORM/g