x86/MCE/AMD: Use an u64 for bank_map

In the Linux kernel, the following vulnerability has been resolved:

x86/MCE/AMD: Use an u64 for bank_map

Thee maximum number of MCA banks is 64 (MAX_NR_BANKS), see

a0bc32b3cacf ("x86/mce: Increase maximum number of banks to 64").

However, the bank_map which contains a bitfield of which banks to
initialize is of type unsigned int and that overflows when those bit
numbers are >= 32, leading to UBSAN complaining correctly:

UBSAN: shift-out-of-bounds in arch/x86/kernel/cpu/mce/amd.c:1365:38
shift exponent 32 is too large for 32-bit type 'int'

Change the bank_map to a u64 and use the proper BIT_ULL() macro when
modifying bits in there.

[ bp: Rewrite commit message. ]