staging: vme: Move 'vme/devices/' to 'vme_user/'

In <db3b9e990e75573402cda22faf933760f076c033> ("Staging: VME: move VME
drivers out of staging") the vme code, board and bridge drivers were
moved out of the staging tree, remaining only the VME user device
driver.

Since this driver is the only one remaining in staging, such multi-level
structure confuses more than helps. The current structure is as follows:

- drivers/staging/vme/
Makefile
devices/
Kconfig
Makefile
vme_user.c
vme_user.h

The top-level Makefile has the only function of calling another Makefile
into the devices/ subdirectory. This latter only compiles the vme_user
driver, since there is no other in the staging tree.

This patch removes the unnecessary Makefile from the 'vme/' dir, move
the contents of 'vme/devices' into the 'vme/' dir, and renames it to
'vme_user/' (the driver name), allowing a straightforward understanding
of this driver's contents. Furthermore, it updates the MAINTAINERS file
to properly reflect the new paths.

Signed-off-by: Bruno Moreira-Guedes <codeagain@codeagain.dev>
Link: https://lore.kernel.org/r/2cd7de9a426c443a5ea618682d605ecfd751d798.1650544175.git.codeagain@codeagain.dev
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>