ARM: kvm: round HYP section to page size instead of log2 upper bound

Older binutils do not support expressions involving the values of
external symbols so just round up the HYP region to the page size.

Tested-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
[will: when will this ever end?!]
Signed-off-by: Will Deacon <will.deacon@arm.com>