Add iomap support including direct I/O

Switch many code paths to use iomap instead of get_block. This includes
buffered reads and writes, llseek, fiemap, and new support for direct
I/O.

Add KC_USE_IOMAP_FOR_IO and only build the iomap R/W pieces
for EL9.5 and higher. We support iomap for fiemap and llseek
on EL8 and EL9.4.

Signed-off-by: Chris Kirby <ckirby@versity.com>

kmod/src/Makefile

@@ -25,6 +25,7 @@ scoutfs-y +=			\
 	forest.o		\
 	inode.o			\
 	ioctl.o			\
+	iomap.o			\
 	item.o			\
 	kernelcompat.o		\
 	lock.o			\