Update Kconfig for ARM64 and add compile tutorial for Odroidn2

init/Kconfig

@@ -2358,7 +2358,7 @@ config ARCH_HAS_SYSCALL_WRAPPER
 
 config SCHED_CLASS_GHOST
 	bool "ghOSt scheduling class"
-	depends on X86_64
+	depends on (X86_64 || ARM64)
 	default n
 	help
 	  ghOSt is a scheduling class with policy decisions delegated

odroidn2_compile.md

@@ -0,0 +1,39 @@
+0. Pre-request:
+    1. [Odroid n2 board](https://www.hardkernel.com/shop/odroid-n2-with-4gbyte-ram/) (n2+ should be fine, but I have not test it yet).
+    2. [Armbian linux image](https://www.armbian.com/odroid-n2/): the version of image I'm using is `Armbian_22.02.2_Odroidn2_focal_current_5.10.103`.
+1. Install required packages
+`
+    $sudo apt-get install git fakeroot build-essential ncurses-dev xz-utils libssl-dev bc flex libelf-dev bison -y
+`
+2. Clone the source code
+`$ git clone https://github.com/google/ghost-kernel.git && cd ghost_kernel`
+3. Copy the config file to source code directory 
+`$ cp /boot/cp /boot/config-5.10.103-meson64 .config `
+4. Remove the signature checking certificates
+`$ make menuconfig`
+Remove 'debian/canonical-certs.pem' in Cryptographic API -> Certificates for signature checking
+5. Start to compile  `make -j4`
+6. Install the kernel module
+`$ sudo make INSTALL_MOD_STRIP=1 modules_install # strip the modules to reduce the size of initrd`
+Or
+```
+    $ sudo make install
+    $ cd /lib/modules/<new_kernel> 
+    $ find . -name *.ko -exec strip --strip-unneeded {} +
+```
+7.  After executing above command, proceed to create initramfs/initrd
+```
+    $ sudo make install
+    $ sudo ln -s vmlinuz-5.11.0+ Image
+```
+8. Reboot and check the version of new kernel
+```
+    $ sudo reboot 
+    $ uname -a to check the kernel
+```
+It should output the new kernel version which is `5.11.0+`: ` Linux ubuntu 5.11.0+ #2 SMP PREEMPT Mon Apr 18 00:50:21 UTC 2022 aarch64 aarch64 aarch64 GNU/Linux`
+
+9. Finally install the headers
+` sudo make headers_install INSTALL_HDR_PATH=/usr`
+
+10. Have fun