UPSTREAM: arm64: introduce KIMAGE_VADDR as the virtual base of the kernel region

UPSTREAM: arm64: introduce KIMAGE_VADDR as the virtual base of the kernel region

This introduces the preprocessor symbol KIMAGE_VADDR which will serve as
the symbolic virtual base of the kernel region, i.e., the kernel's virtual
offset will be KIMAGE_VADDR + TEXT_OFFSET. For now, we define it as being
equal to PAGE_OFFSET, but in the future, it will be moved below it once
we move the kernel virtual mapping out of the linear mapping.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Bug: 30369029
Patchset: kaslr-arm64-4.4

(cherry picked from commit ab893fb9f1b17f02139bce547bb4b69e96b9ae16)
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Change-Id: I31427bd2b948a22bb8ce1d22109682fc66efb98d