riscv: cpu: check and append L1 cache to cpu features

All cpu cores within FU540-C000 having split I/D caches.
Set the L1 cache feature bit using the i-cache-size or d-cache-size
as one of the property from device tree indicating that L1 cache is
present on the cpu core.

=> cpu detail
  1: cpu@1      rv64imafdc
        ID = 1, freq = 999.100 MHz: L1 cache, MMU
  2: cpu@2      rv64imafdc
        ID = 2, freq = 999.100 MHz: L1 cache, MMU
  3: cpu@3      rv64imafdc
        ID = 3, freq = 999.100 MHz: L1 cache, MMU
  4: cpu@4      rv64imafdc
        ID = 4, freq = 999.100 MHz: L1 cache, MMU

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>