Add support for AArch32

Add support for AArch32

gcc version 4.9.2 (Raspbian 4.9.2-10)
Tested on Linux raspberrypi 4.4.6-v7+ #875 SMP Tue Apr 12 16:33:02 BST 2016 armv7l GNU/Linux

CPUs may be little or big endian, detect with gcc flags, not the processor architecture
Add a new flag $(PLATFORM)_uses_openssl which allows to disable the link with openssl lib.

vlib/vlib/threads.c:
startup.conf must:
- specify the heapsize as we don't have hugepages on raspbian

cpu {
  main-core 3
}
heapsize 64M

Corrects in various files the assumption uword == u64 and replaces 'u64' cast with 'pointer_to_uword' and 'uword_to_pointer' where appropriate.
256 CPUs may create an OOM when testing with small memory footprint ( heapsize 64M ), allows the number of VLIB_MAX_CPUS to be set in platforms/*.mk

vppinfra/vppinfra/longjmp.S:
ARM - copy r1 (1st parameter of the setjmp call) to r0 (return value)

vppinfra/vppinfra/time.h:
On ARMv7 in AArch32 mode, we can access to a 64bit register to retreive the cycles count.
gcc on rpi only declare ARM_ARCH 6. Override this info, and check if it is possible to use 'mrrc'.
/!\ the time function will NOT work without allowing the user mode access to the PMU.
You may download the source of the kmod here:
https://github.com/christophefontaine/arm_rdtsc

Change-Id: I8142606436d9671a184133b935398427f08a8bd2
Signed-off-by: Christophe Fontaine <christophe.fontaine@qosmos.com>