accel/kvm: avoid using predefined PAGE_SIZE

accel/kvm: avoid using predefined PAGE_SIZE

As per POSIX specification of limits.h [1], OS libc may define
PAGE_SIZE in limits.h.

PAGE_SIZE is used in included kernel uapi headers.

To prevent collosion of definition, we discard PAGE_SIZE from
defined by libc and take QEMU's variable.

[1]: https://pubs.opengroup.org/onlinepubs/7908799/xsh/limits.h.html

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Message-Id: <20210118063808.12471-8-jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>