x86/platform/uv: Provide is_early_uv_system()

Introduce is_early_uv_system() which uses efi.uv_systab to decide early
in the boot process whether the kernel runs on a UV system.

This is needed to skip other early setup/init code that might break
the UV platform if done too early such as before necessary ACPI tables
parsing takes place.

Suggested-by: Hedi Berriche <hedi.berriche@hpe.com>
Signed-off-by: Mike Travis <mike.travis@hpe.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Russ Anderson <rja@hpe.com>
Reviewed-by: Dimitri Sivanich <sivanich@hpe.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Russ Anderson <russ.anderson@hpe.com>
Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Len Brown <len.brown@intel.com>
Cc: Dou Liyang <douly.fnst@cn.fujitsu.com>
Cc: Xiaoming Gao <gxm.linux.kernel@gmail.com>
Cc: Rajvi Jingar <rajvi.jingar@intel.com>
Link: https://lkml.kernel.org/r/20181002180144.801700401@stormcage.americas.sgi.com

arch/x86/include/asm/uv/uv.h

@@ -10,8 +10,13 @@ struct cpumask;
 struct mm_struct;
 
 #ifdef CONFIG_X86_UV
+#include <linux/efi.h>
 
 extern enum uv_system_type get_uv_system_type(void);
+static inline bool is_early_uv_system(void)
+{
+	return !((efi.uv_systab == EFI_INVALID_TABLE_ADDR) || !efi.uv_systab);
+}
 extern int is_uv_system(void);
 extern int is_uv_hubless(void);
 extern void uv_cpu_init(void);
@@ -23,6 +28,7 @@ extern const struct cpumask *uv_flush_tlb_others(const struct cpumask *cpumask,
 #else	/* X86_UV */
 
 static inline enum uv_system_type get_uv_system_type(void) { return UV_NONE; }
+static inline bool is_early_uv_system(void)	{ return 0; }
 static inline int is_uv_system(void)	{ return 0; }
 static inline int is_uv_hubless(void)	{ return 0; }
 static inline void uv_cpu_init(void)	{ }