ARM: kvm: assert on HYP section boundaries not actual code size

Using ASSERT() with an expression that involves a symbol that
is only supplied through a PROVIDE() definition in the linker
script itself is apparently not supported by some older versions
of binutils.

So instead, rewrite the expression so that only the section
boundaries __hyp_idmap_text_start and __hyp_idmap_text_end
are used. Note that this reverts the fix in 06f75a1f
("ARM, arm64: kvm: get rid of the bounce page") for the ASSERT()
being triggered erroneously when unrelated linker emitted veneers
happen to end up in the HYP idmap region.
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm/kernel/vmlinux.lds.S

@@ -381,5 +381,5 @@ ASSERT((__arch_info_end - __arch_info_begin), "no machine record defined")
  * and should not cross a page boundary.
  * The above comment applies as well.
  */
-ASSERT((__hyp_idmap_text_start & ~PAGE_MASK) + __hyp_idmap_size <= PAGE_SIZE,
+ASSERT(__hyp_idmap_text_end - (__hyp_idmap_text_start & PAGE_MASK) <= PAGE_SIZE,
 	"HYP init code too big or misaligned")