arm64: hibernate: rename dst to page in create_safe_exec_page

create_safe_exec_page() allocates a safe page and maps it at a
specific location, also this function returns the physical address
of newly allocated page.

The destination VA, and PA are specified in arguments: dst_addr,
phys_dst_addr

However, within the function it uses "dst" which has unsigned long
type, but is actually a pointers in the current virtual space. This
is confusing to read.

Rename dst to more appropriate page (page that is created), and also
change its time to "void *"

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>