x86: Add an enum for some commonly-used GDT bits

Rather than add these as open-coded values, create an enum with the commonly
used flags.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/x86/include/asm/cpu.h

@@ -27,6 +27,24 @@ enum {
 	X86_VENDOR_UNKNOWN = 0xff
 };
 
+/* Global descriptor table (GDT) bits */
+enum {
+	GDT_4KB			= 1ULL << 55,
+	GDT_32BIT		= 1ULL << 54,
+	GDT_LONG		= 1ULL << 53,
+	GDT_PRESENT		= 1ULL << 47,
+	GDT_NOTSYS		= 1ULL << 44,
+	GDT_CODE		= 1ULL << 43,
+	GDT_LIMIT_LOW_SHIFT	= 0,
+	GDT_LIMIT_LOW_MASK	= 0xffff,
+	GDT_LIMIT_HIGH_SHIFT	= 48,
+	GDT_LIMIT_HIGH_MASK	= 0xf,
+	GDT_BASE_LOW_SHIFT	= 16,
+	GDT_BASE_LOW_MASK	= 0xffff,
+	GDT_BASE_HIGH_SHIFT	= 56,
+	GDT_BASE_HIGH_MASK	= 0xf,
+};
+
 struct cpuid_result {
 	uint32_t eax;
 	uint32_t ebx;