Mark `inline` function as `static`

In c99 a function that is just `inline` needs an `extern` declaration somewhere so that
the compiler knows where to generate the non inlined version of the function for linking.
As this function has no `extern` declaration the compiler, depending on optimisation
levels, may emit a call to the function instead of inline, which will result in a link
time failure as none is generated.

libsel4vmm/src/processor/lapic.c

diff --git a/libsel4vmm/src/processor/lapic.c b/libsel4vmm/src/processor/lapic.c
index 1d673ff..03943af 100644
--- a/libsel4vmm/src/processor/lapic.c
+++ b/libsel4vmm/src/processor/lapic.c
@@ -122,7 +122,7 @@
     *((uint32_t *) (apic->regs + reg_off)) = val;
 }
 
-inline uint32_t vmm_apic_get_reg(vmm_lapic_t *apic, int reg_off)
+static inline uint32_t vmm_apic_get_reg(vmm_lapic_t *apic, int reg_off)
 {
     return *((uint32_t *) (apic->regs + reg_off));
 }
@@ -150,12 +150,12 @@
     ((uint32_t *)bitmap)[vec >> 5] &= ~(1UL << (vec & 31));
 }
 
-inline int vmm_apic_sw_enabled(vmm_lapic_t *apic)
+static inline int vmm_apic_sw_enabled(vmm_lapic_t *apic)
 {
     return vmm_apic_get_reg(apic, APIC_SPIV) & APIC_SPIV_APIC_ENABLED;
 }
 
-inline int vmm_apic_hw_enabled(vmm_lapic_t *apic)
+static inline int vmm_apic_hw_enabled(vmm_lapic_t *apic)
 {
     return apic->apic_base & MSR_IA32_APICBASE_ENABLE;
 }