Fix C accessors to GIC distributor registers with set/clear semantics

This patch fixes C accessors to GIC registers that follow a set/clear
semantic to change the state of an interrupt, instead of read/write/modify.
These registers are:
  Set-Enable
  Clear-Enable
  Set-Pending
  Clear-Pending
  Set-Active
  Clear-Active
For instance, to enable an interrupt we write a one to the corresponding bit
in the Set-Enable register, whereas to disable it we write a one to the
corresponding bit in the Clear-Enable register.

Fixes ARM-software/tf-issues#137

Change-Id: I3b66bad94d0b28e0fe08c9042bac0bf5ffa07944

drivers/arm/gic/gic_v2.c

@@ -214,49 +214,43 @@ void gicd_clr_igroupr(unsigned int base, unsigned int id)
 void gicd_set_isenabler(unsigned int base, unsigned int id)
 {
 	unsigned bit_num = id & ((1 << ISENABLER_SHIFT) - 1);
-	unsigned int reg_val = gicd_read_isenabler(base, id);
 
-	gicd_write_isenabler(base, id, reg_val | (1 << bit_num));
+	gicd_write_isenabler(base, id, (1 << bit_num));
 }
 
 void gicd_set_icenabler(unsigned int base, unsigned int id)
 {
 	unsigned bit_num = id & ((1 << ICENABLER_SHIFT) - 1);
-	unsigned int reg_val = gicd_read_icenabler(base, id);
 
-	gicd_write_icenabler(base, id, reg_val & ~(1 << bit_num));
+	gicd_write_icenabler(base, id, (1 << bit_num));
 }
 
 void gicd_set_ispendr(unsigned int base, unsigned int id)
 {
 	unsigned bit_num = id & ((1 << ISPENDR_SHIFT) - 1);
-	unsigned int reg_val = gicd_read_ispendr(base, id);
 
-	gicd_write_ispendr(base, id, reg_val | (1 << bit_num));
+	gicd_write_ispendr(base, id, (1 << bit_num));
 }
 
 void gicd_set_icpendr(unsigned int base, unsigned int id)
 {
 	unsigned bit_num = id & ((1 << ICPENDR_SHIFT) - 1);
-	unsigned int reg_val = gicd_read_icpendr(base, id);
 
-	gicd_write_icpendr(base, id, reg_val & ~(1 << bit_num));
+	gicd_write_icpendr(base, id, (1 << bit_num));
 }
 
 void gicd_set_isactiver(unsigned int base, unsigned int id)
 {
 	unsigned bit_num = id & ((1 << ISACTIVER_SHIFT) - 1);
-	unsigned int reg_val = gicd_read_isactiver(base, id);
 
-	gicd_write_isactiver(base, id, reg_val | (1 << bit_num));
+	gicd_write_isactiver(base, id, (1 << bit_num));
 }
 
 void gicd_set_icactiver(unsigned int base, unsigned int id)
 {
 	unsigned bit_num = id & ((1 << ICACTIVER_SHIFT) - 1);
-	unsigned int reg_val = gicd_read_icactiver(base, id);
 
-	gicd_write_icactiver(base, id, reg_val & ~(1 << bit_num));
+	gicd_write_icactiver(base, id, (1 << bit_num));
 }
 
 /*