arch: arc: add handling for accl regs, r25, r30

* when fpu is configured or mpy_option > 6,
accl regs (r58, r59) will be configured,
they are used by fpu and mac, and are caller
-saved scratch regs, so need to be saved before
jumping to interrupt handlers

* r25 and r30 are also caller-saved scratch reg.

Signed-off-by: Wayne Ren <wei.ren@synopsys.com>