portable/chipidea: name SBUSCFG in ci_hs_regs_t, unify AHB burst hook

Replace the duplicated per-MCU dispatch in dcd_init/hcd_init and the two
helper flavors (USB_Type access on iMX RT, raw offset 0x90 on LPC18/43)
with one SBUSCFG register field plus a per-header CI_HS_SET_AHB_BURST()
hook, compiled only where defined. The LPC USB0-only policy is now
visible at the macro definition.