Revert "console: simplify puts()"

Revert "console: simplify puts()"

This reverts commit c61d0009feb966e0e93254a8c435a1889085e6b8.

A tbs2910 board user reported a very slow console frambuffer as
regression in current u-boot. I could bisect this down to the
above mentioned commit.

This revert brings back the fast framebuffer console (one
cache flush per string in puts(), not after each char).

Reported-by: Uwe Scheffler <[email protected]>
Signed-off-by: Soeren Moch <[email protected]>
Tested-by: Uwe Scheffler <[email protected]>
Reviewed-by: Simon Glass <[email protected]>