x86/page: Remove bifurcated PAGE_HYPERVISOR constant

x86/page: Remove bifurcated PAGE_HYPERVISOR constant

Despite being vaguely aware, the difference between PAGE_HYPERVISOR in ASM and
C code has nevertheless caused several bugs I should have known better about,
and contributed to review confusion.

There are exactly 4 uses of these constants in asm code (and one is shortly
going to disappear).

Instead of creating the constants which behave differently between ASM and C
code, expose all the constants and use non-ambiguous non-NX ones in ASM.
Adjust the hiding to just _PAGE_NX, which contains a C ternary expression.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>