zram: remove zram_sysfs file (v2)

(cherry pick from commit 9b3bb7abcdf2df0f1b2657e6cbc9d06bc2b3b36f)

Move zram sysfs code to zram drv and remove zram_sysfs.c
file. This gives ability to make static a number of previously
exported zram functions, used from zram sysfs, e.g. internal zram
zram_meta_alloc/free(). We also can drop zram_drv wrapper
functions, used from zram sysfs:
e.g. zram_reset_device()/__zram_reset_device() pair.

v2: as suggested by Greg K-H, move MODULE description to the
bottom of the file.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Bug: 24810447
Change-Id: Ic0038af190db194f7891cb27502a9b6d0d9e4042