Raspberry Pi 4 with 32 bit Raspbian isn't detected as ARMV6

[SeanTAllen]

trafficstars

in platform.h we have a number of compiler definition checks and set ARMV6.

The definition is only used on 1 place in the codebase; in cpu.c to turn on code to check to see if a hardware cycle counter is available. The Raspberry Pi 4 should be being marked as ARMV6.

This likely impacts on some other Arm platforms as well.

• 32 bit Raspbian
• Raspberry Pi 4

This still needs to be tested on 64-bit Arm to see if it also impacts there.

When this is fixed, release notes should be added and the PR marked as "CHANGELOG - Fixed". This has a definite performance impact on any Arm platform where the hardware cycle counter is available. Sadly, on the Pi, its a privileged operation to read, so there will be no performance impact there.