package/freerdp: do not use Neon extensions when not available

FreeRDP mis-detects the CPU, and may enable Neon extensions when it
should not. Not all ARM processors have Neon extensions.

Heck, what's more, none non-ARM processor has Neon extensions!
The regexp to detect the CPU is borked:  'arm*'  will also match 'arc'
as well as 'arm'.

Do not let FreeRDP try to decide if it can use Neon extensions, we have
a Kconfig option for that, that we can use to force FreeRDP to use it or
not.

Should fix:
    http://autobuild.buildroot.org/results/d4a/d4a61e686cf11d993d02ece0c4e2835a926603c2/
    http://autobuild.buildroot.org/results/234/2349d40ef8d658ab1cd7332eb1b42a75afcd423f/


   ...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>