xen: arm: Correctly use GLOBAL/ENTRY in head.S, avoid .global

xen: arm: Correctly use GLOBAL/ENTRY in head.S, avoid .global

Use ENTRY() for function entry points since it ensures correct
alignment where GLOBAL() doesn't. The exception is the initial start
label which must be at offset 0, so just use GLOBAL() to avoid the
possibility of realignment.

Since everything happens to already be aligned there should be no
difference to the actual binary. objdump agrees.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Julien Grall <julien.grall@linaro.org>