linux-tools: perf: add option to build TUI

linux-tools: perf: add option to build TUI

Since Linux 3.10, perf's NO_NEWT configuration option simply sets
NO_SLANG=1 and there is no dependency on libnewt.

We already handle NO_SLANG correctly based on whether or not
BR2_PACKAGE_SLANG is selected, so all we accomplish by setting NO_NEWT=1
is disabling perf's TUI when all of the dependencies are available.

To simplify all of this, introduce a new config option to enable the
perf TUI which depends on slang and add a check to prevent building the
TUI on versions which are too old.  The check for NO_SLANG is equivalent
to checking if NO_NEWT is required as NO_SLANG was added in the same
commit that removed the libnewt dependency and deprecated NO_NEWT
(6692c262df4f, "perf tools: Remove dependency on libnewt", 2013-03-28).

Signed-off-by: John Keeping <john@metanate.com>
[Thomas: add missing BR2_USE_MMU dependency, coming from the slang
package. Noticed by Yann E. Morin.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>