ext/hal/st/stm32cube/stm32l1xx: rename SVC_IRQn -> SVCall_IRQn

SVCall_IRQn is used as enum value for SV Call Interrupt for Cortex-M
based SoCs for which CPU_CORTEX_M_HAS_BASEPRI=y. However stm32cube
for stm32l1xx uses SVC_IRQn enum value for this purpose.
This leads to this error:

  arch/arm/include/cortex_m/exc.h:101:19: error: 'SVCall_IRQn'
    undeclared (first use in this function); did you mean 'SVC_IRQn'?

    NVIC_SetPriority(SVCall_IRQn, _EXC_SVC_PRIO);
                     ^~~~~~~~~~~
                     SVC_IRQn

NB: ext/hal/st/stm32cube/stm32l1xx/soc/stm32l151xb.h file was already
fixed in 9f8260457b86 ('ext: hal: st: stm32cube: Add HAL for
the STM32L1x series').

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>