lib: sbi: pmu: fix usage of sbi_pmu_irq_bit()

While sbi_pmu_irq_bit() was used to delegate irq to S-mode, LCOFIP usage
was still hardcoded in various places. This led to change the returned
value of sbi_pmu_irq_bit() to be a bit number rather than a bit mask
since it returns an 'int' and we need to obtain the bit number itself to
handle it in the IRQs handlers. Add a similar function to return the
irq mask which can also be used where the mask is required rather than
the bit itself.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>

platform/generic/include/thead/c9xx_encoding.h

@@ -122,6 +122,5 @@
 
 /* T-HEAD C9xx MIP CSR extension */
 #define THEAD_C9XX_IRQ_PMU_OVF		17
-#define THEAD_C9XX_MIP_MOIP		(_UL(1) << THEAD_C9XX_IRQ_PMU_OVF)
 
 #endif