x86/APIC: command line option adjustments

Improving their documentation, and converting one option to boolean
since it has only boolean meaning.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -674,6 +674,10 @@ debug hypervisor only).
 > `= <integer>`
 
 ### ioapic\_ack
+> `= old | new`
+
+> Default: `new` unless directed-EOI is supported
+
 ### iommu
 > `= List of [ <boolean> | force | required | intremap | qinval | snoop | sharept | dom0-passthrough | dom0-strict | amd-iommu-perdev-intremap | workaround_bios_bug | verbose | debug ]`
 
@@ -789,10 +793,10 @@ Force the use of `[<seg>:]<bus>:<device>
 ACPI table.
 
 ### lapic
+> `= <boolean>`
 
 Force the use of use of the local APIC on a uniprocessor system, even
-if left disabled by the BIOS.  This option will accept any value at
-all.
+if left disabled by the BIOS.
 
 ### lapic\_timer\_c2\_ok
 > `= <boolean>`
@@ -834,6 +838,9 @@ uses.  The limit only applies to the hig
 ### max\_gsi\_irqs
 > `= <integer>`
 
+Specifies the number of interrupts to be use for pin (IO-APIC or legacy PIC)
+based interrupts. Any higher IRQs will be available for use via PCI MSI.
+
 ### maxcpus
 > `= <integer>`
 
@@ -918,7 +925,7 @@ IRQ routing issues.
 > Default: `false`
 
 Ignore the local APIC on a uniprocessor system, even if enabled by the
-BIOS.  This option will accept value.
+BIOS.
 
 ### no-real-mode (x86)
 > `= <boolean>`
--- a/xen/arch/x86/apic.c
+++ b/xen/arch/x86/apic.c
@@ -813,12 +813,7 @@ static void __init lapic_disable(char *s
     setup_clear_cpu_cap(X86_FEATURE_APIC);
 }
 custom_param("nolapic", lapic_disable);
-
-static void __init lapic_enable(char *str)
-{
-    enable_local_apic = 1;
-}
-custom_param("lapic", lapic_enable);
+boolean_param("lapic", enable_local_apic);
 
 static void __init apic_set_verbosity(char *str)
 {