i965/fs: Add byte scattered write message and fs support

i965/fs: Add byte scattered write message and fs support

v2: (Jason Ekstrand)
    - Enable bit_size parameter to scattered messages to enable different
      bitsizes byte/word/dword.
    - Remove use of brw_send_indirect_scattered_message in favor of
      brw_send_indirect_surface_message.
    - Move scattered messages to surface messages namespace.
    - Assert align1 for scattered messages and assume Gen8+.
    - Inline brw_set_dp_byte_scattered_write.
v3: - Remove leftover newline (Topi Pohjolainen)
    - Rename brw_data_size to brw_scattered_data_element and use
      defines instead of an enum (Jason Ekstrand)
    - Assert scattered write for Gen8+ and Haswell (Jason Ekstrand)

Signed-off-by: Jose Maria Casanova Crespo <jmcasanova@igalia.com>
Signed-off-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>