[LinuxBIOS] more safe stack in ram for cache_as_ram

[YhLu]

just committed some change for cache_as_ram

in every cache_as_ram_auto.c
        __asm__ volatile (
                /* set new esp */ /* before _RAMBASE */
                "movl   %0, %%ebp\n\t"
                "movl   %0, %%esp\n\t"
                ::"a"( _RAMBASE -4 )
        );

        ====>

        __asm__ volatile (
                /* set new esp */ /* before _RAMBASE */
                "subl   %0, %%ebp\n\t"
                "subl   %0, %%esp\n\t"
                ::"a"( (DCACHE_RAM_BASE + DCACHE_RAM_SIZE)- _RAMBASE )
        );


YH