tools/x86/kcpuid: Set max possible subleaves count to 64

cpuid.csv will be extended in further commits with all-publicly-known
CPUID leaves and bitfields.  One of the new leaves is 0xd for extended
CPU state enumeration.  Depending on XCR0 dword bits, it can export up to
64 subleaves.

Set kcpuid.c MAX_SUBLEAF_NUM to 64.

Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240718134755.378115-4-darwi@linutronix.de