arm64: kasan: abstract _text and _end to KERNEL_START/END

Arm64 provides defined macro for KERNEL_START and KERNEL_END,
thus replace them by the abstration instead of using _text and _end.

Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
Acked-by: Andrey Konovalov <andreyknvl@gmail.com>
Tested-by: Andrey Konovalov <andreyknvl@gmail.com>
Tested-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20210324040522.15548-3-lecopzer.chen@mediatek.com


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>