lib: utils/fdt: Fix fdt_parse_isa_extensions() implementation

Currently, the fdt_parse_isa_extensions() tries to parse the ISA
string once for each HART. This ISA string parsing can fail for
secondary HARTs if the FDT memory is already overwritten by the
supervisor OS.

To tackle this issue, we improve the fdt_parse_isa_extensions()
implementation to pre-parse ISA string for all HARTs during
cold boot.

Fixes: d72f5f17

 ("lib: utils: Add detection of Smepmp from ISA
string in FDT")
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Tested-By: Mayuresh <Chitale&lt;mchitale@ventanamicro.com>