uclass: cpu: fix to display proper CPU features

The cmd "cpu detail" fetches uninitialized cpu feature information
and thus displays wrong / inconsitent details as below.
For eg: FU540-C000 doesn't have any microcode, yet the cmd display's it.

=> cpu detail
  1: cpu@1      rv64imafdc
        ID = 1, freq = 999.100 MHz: L1 cache, MMU, Microcode, Device ID
        Microcode version 0x0
        Device ID 0x0
  2: cpu@2      rv64imafdc
        ID = 2, freq = 999.100 MHz: L1 cache, MMU, Microcode, Device ID
        Microcode version 0x0
        Device ID 0x0
  3: cpu@3      rv64imafdc
        ID = 3, freq = 999.100 MHz: L1 cache, MMU, Microcode, Device ID
        Microcode version 0x0
        Device ID 0x0
  4: cpu@4      rv64imafdc
        ID = 4, freq = 999.100 MHz: L1 cache, MMU, Microcode, Device ID
        Microcode version 0x0
        Device ID 0x0

The L1 cache or MMU entry seen above is also displayed inconsistently.
So initialize cpu information to zero into cpu-uclass itself so that
similar issues can be avoided for other CPU drivers.

We now see correct features as:
=> cpu detail
  1: cpu@1      rv64imafdc
        ID = 1, freq = 999.100 MHz
  2: cpu@2      rv64imafdc
        ID = 2, freq = 999.100 MHz
  3: cpu@3      rv64imafdc
        ID = 3, freq = 999.100 MHz
  4: cpu@4      rv64imafdc
        ID = 4, freq = 999.100 MHz

Signed-off-by: Sagar Shrikant Kadam <sagar.kadam@sifive.com>
Reviewed-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>