Use the existing generator macros to create deferred-I/O helpers
for broadsheetfb and set them in the fb_ops structure. Functions
for damage handling on memory ranges and areas are provided by
the driver.

Broadsheedfb's implementation of fb_write writes to system memory,
so the generated code can use the respective helper internally.
This also fixes a long-standing bug where fb_write returned an
errno code instead of the number of written bytes. See the commit
message of commit 921b7383 ("fbdev: Return number of bytes
read or written") for more details.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230706151432.20674-3-tzimmermann@suse.de