kernel: refactor aarch64 boot code

Signed-off-by: EnderIce2 <enderice2@protonmail.com>

Kernel/arch/aarch64/bootstrap/raspi/boot.S

@@ -0,0 +1,49 @@
+/*
+	This file is part of Fennix Kernel.
+
+	Fennix Kernel is free software: you can redistribute it and/or
+	modify it under the terms of the GNU General Public License as
+	published by the Free Software Foundation, either version 3 of
+	the License, or (at your option) any later version.
+
+	Fennix Kernel is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with Fennix Kernel. If not, see <https://www.gnu.org/licenses/>.
+*/
+
+.section ".bootstrap.boot", "a"
+
+.extern _kernel_bss_start
+.extern _kernel_bss_end
+.extern _kernel_bss_size
+
+.global _start
+_start:
+	/* Keep only the main core */
+	mrs x1, mpidr_el1
+	and x1, x1, #3
+	cbz x1, 2f
+
+	/* Halt */
+1:	wfe
+	b 1b
+
+	/* Initialize the stack */
+2:	ldr x1, =_start
+	mov sp, x1
+
+	/* Clear the BSS */
+	ldr x1, =_kernel_bss_start
+	ldr w2, =_kernel_bss_size
+3:	cbz w2, 4f
+	str xzr, [x1], #8
+	sub w2, w2, #1
+	cbnz w2, 3b
+
+	/* Start the kernel */
+4:	bl _aarch64_start
+	b 1b