Raise armv8r-none-eabihf to Tier 2

This is the target for supporting Arm Cortex-R52 bare-metal systems,
which are common in safety-critical systems.

Author: thejpster

src/doc/rustc/src/platform-support.md

@@ -167,6 +167,7 @@ target | std | notes
 [`armv7a-none-eabi`](platform-support/armv7a-none-eabi.md) | * | Bare Armv7-A
 [`armv7r-none-eabi`](platform-support/armv7r-none-eabi.md) | * | Bare Armv7-R
 [`armv7r-none-eabihf`](platform-support/armv7r-none-eabi.md) | * | Bare Armv7-R, hardfloat
+[`armv8r-none-eabihf`](platform-support/armv8r-none-eabihf.md) | * |  | Bare Armv8-R, hardfloat
 `i586-unknown-linux-gnu` | ✓ | 32-bit Linux (kernel 3.2+, glibc 2.17, original Pentium) [^x86_32-floats-x87]
 `i586-unknown-linux-musl` | ✓ | 32-bit Linux (musl 1.2.3, original Pentium) [^x86_32-floats-x87]
 [`i686-linux-android`](platform-support/android.md) | ✓ | 32-bit x86 Android ([Pentium 4 plus various extensions](https://developer.android.com/ndk/guides/abis.html#x86)) [^x86_32-floats-return-ABI]
@@ -304,7 +305,6 @@ target | std | host | notes
 [`armv7a-vex-v5`](platform-support/armv7a-vex-v5.md) | ? |  | Armv7-A Cortex-A9 VEX V5 Brain, VEXos
 [`armv7k-apple-watchos`](platform-support/apple-watchos.md) | ✓ |  | Armv7-A Apple WatchOS
 [`armv7s-apple-ios`](platform-support/apple-ios.md) | ✓ |  | Armv7-A Apple-A6 Apple iOS
-[`armv8r-none-eabihf`](platform-support/armv8r-none-eabihf.md) | * |  | Bare Armv8-R, hardfloat
 [`armv7a-nuttx-eabi`](platform-support/nuttx.md) | ✓ |  | ARMv7-A with NuttX
 [`armv7a-nuttx-eabihf`](platform-support/nuttx.md) | ✓ |  | ARMv7-A with NuttX, hardfloat
 [`avr-none`](platform-support/avr-none.md) | * |  | AVR; requires `-Zbuild-std=core` and `-Ctarget-cpu=...`

src/doc/rustc/src/platform-support/armv8r-none-eabihf.md

@@ -1,6 +1,6 @@
 # `armv8r-none-eabihf`
 
-* **Tier: 3**
+* **Tier: 2**
 * **Library Support:** core and alloc (bare-metal, `#![no_std]`)
 
 Bare-metal target for CPUs in the Armv8-R architecture family, supporting