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>

tests/src/mmap_stress.c

@@ -80,7 +80,7 @@ static void *run_test_func(void *ptr)
 			for (read = 0; read < size;) {
 				ret = pread(fd, buf, size - read, read);
 				if (ret < 0) {
-					perror("pwrite");
+					perror("pread");
 					exit(-1);
 				}
 				read += ret;