NFSv4.1: unify pnfs_pageio_init functions

Use common code for pnfs_pageio_init_{read,write} and use
a common generic pg_test function.

Note that this function always assumes the the layout driver's
pg_test method is implemented.

[Fix BUG]
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>

diff --cc fs/nfs/pagelist.c
Simple merge

diff --cc fs/nfs/pnfs.c
Simple merge

diff --cc fs/nfs/pnfs.h
Simple merge

diff --cc fs/nfs/read.c
Simple merge

diff --cc fs/nfs/write.c
Simple merge