x86/entry: Correct comparisons against boolean variables

x86/entry: Correct comparisons against boolean variables

The correct way to check a boolean is `cmpb $0` or `testb $0xff`, whereas a
lot of our entry code uses `testb $1`.  This will work in principle for values
which are really C _Bool types, but won't work for other integer types which
are intended to have boolean properties.

cmp is the more logical way of thinking about the operation, so adjust all
outstanding uses of `testb $1` against boolean values.  Changing test to cmp
changes the logical mnemonic of the following condition from 'zero' to
'equal', but the actual encoding remains the same.

No functional change, as all uses are real C _Bool types, and confirmed by
diffing the disassembly.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>